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 $68.46   9.584%   $75.0212   $75.02   $75.00   $75.00  
  Purchase #2 $240.28   12.742%   $270.8965   $270.90   $270.90   $270.90  
  Purchase #3 $26.51   4.632%   $27.7379   $27.74   $27.75   $27.70  
  Purchase #4 $157.27   4.206%   $163.8848   $163.88   $163.90   $163.90  
  Purchase #5 $228.25   12.630%   $257.078   $257.08   $257.10   $257.10  
  Purchase #6 $82.79   5.369%   $87.235   $87.24   $87.25   $87.20  
  Purchase #7 $82.30   4.586%   $86.0743   $86.07   $86.05   $86.10  
  7 purchase totals = $885.86       $967.9277   $967.93   $967.95   $967.90