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 $94.52   12.722%   $106.5448   $106.54   $106.55   $106.50  
  Purchase #2 $179.34   3.648%   $185.8823   $185.88   $185.90   $185.90  
  Purchase #3 $152.37   12.755%   $171.8048   $171.80   $171.80   $171.80  
  Purchase #4 $182.91   3.582%   $189.4618   $189.46   $189.45   $189.50  
  Purchase #5 $34.57   4.206%   $36.024   $36.02   $36.00   $36.00  
  Purchase #6 $240.68   12.770%   $271.4148   $271.41   $271.40   $271.40  
  Purchase #7 $111.27   3.413%   $115.0676   $115.07   $115.05   $115.10  
  7 purchase totals = $995.66       $1,076.2001   $1,076.18   $1,076.15   $1,076.20