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 $156.62   12.553%   $176.2805   $176.28   $176.30   $176.30  
  Purchase #2 $155.79   3.604%   $161.4047   $161.40   $161.40   $161.40  
  Purchase #3 $194.82   6.755%   $207.9801   $207.98   $208.00   $208.00  
  Purchase #4 $126.93   7.567%   $136.5348   $136.53   $136.55   $136.50  
  Purchase #5 $170.88   11.439%   $190.427   $190.43   $190.45   $190.40  
  Purchase #6 $180.51   4.397%   $188.447   $188.45   $188.45   $188.40  
  Purchase #7 $26.77   3.658%   $27.7492   $27.75   $27.75   $27.70  
  7 purchase totals = $1,012.32       $1,088.8233   $1,088.82   $1,088.90   $1,088.70