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 $246.33   11.230%   $273.9929   $273.99   $274.00   $274.00  
  Purchase #2 $172.71   11.589%   $192.7254   $192.73   $192.75   $192.70  
  Purchase #3 $86.46   12.422%   $97.2001   $97.20   $97.20   $97.20  
  Purchase #4 $77.94   6.279%   $82.8339   $82.83   $82.85   $82.80  
  Purchase #5 $146.33   12.855%   $165.1407   $165.14   $165.15   $165.10  
  Purchase #6 $150.35   12.349%   $168.9167   $168.92   $168.90   $168.90  
  Purchase #7 $172.93   6.129%   $183.5289   $183.53   $183.55   $183.50  
  7 purchase totals = $1,053.05       $1,164.3386   $1,164.34   $1,164.40   $1,164.20