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 $58.70   13.569%   $66.665   $66.67   $66.65   $66.70  
  Purchase #2 $245.39   6.299%   $260.8471   $260.85   $260.85   $260.80  
  Purchase #3 $178.81   8.717%   $194.3969   $194.40   $194.40   $194.40  
  Purchase #4 $243.57   9.336%   $266.3097   $266.31   $266.30   $266.30  
  Purchase #5 $104.38   5.238%   $109.8474   $109.85   $109.85   $109.80  
  Purchase #6 $209.92   10.694%   $232.3688   $232.37   $232.35   $232.40  
  Purchase #7 $68.75   7.631%   $73.9963   $74.00   $74.00   $74.00  
  7 purchase totals = $1,109.52       $1,204.4312   $1,204.45   $1,204.40   $1,204.40