Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $112.27   10.699%   $124.2818   $124.28   $124.30   $124.30  
  Purchase #2 $247.95   9.631%   $271.8301   $271.83   $271.85   $271.80  
  Purchase #3 $167.32   13.395%   $189.7325   $189.73   $189.75   $189.70  
  Purchase #4 $153.94   9.477%   $168.5289   $168.53   $168.55   $168.50  
  Purchase #5 $176.75   11.116%   $196.3975   $196.40   $196.40   $196.40  
  Purchase #6 $206.31   9.633%   $226.1838   $226.18   $226.20   $226.20  
  Purchase #7 $160.65   5.201%   $169.0054   $169.01   $169.00   $169.00  
  7 purchase totals = $1,225.19       $1,345.9600   $1,345.96   $1,346.05   $1,345.90