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 $56.69   3.341%   $58.584   $58.58   $58.60   $58.60  
  Purchase #2 $207.34   5.411%   $218.5592   $218.56   $218.55   $218.60  
  Purchase #3 $25.73   4.792%   $26.963   $26.96   $26.95   $27.00  
  Purchase #4 $151.55   9.403%   $165.8002   $165.80   $165.80   $165.80  
  Purchase #5 $215.48   8.504%   $233.8044   $233.80   $233.80   $233.80  
  Purchase #6 $64.54   11.559%   $72.0002   $72.00   $72.00   $72.00  
  Purchase #7 $193.63   3.631%   $200.6607   $200.66   $200.65   $200.70  
  7 purchase totals = $914.96       $976.3717   $976.36   $976.35   $976.50