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 $56.28   7.604%   $60.5595   $60.56   $60.55   $60.60  
  Purchase #2 $222.45   5.846%   $235.4544   $235.45   $235.45   $235.50  
  Purchase #3 $131.50   4.386%   $137.2676   $137.27   $137.25   $137.30  
  Purchase #4 $110.96   11.346%   $123.5495   $123.55   $123.55   $123.50  
  Purchase #5 $63.44   11.168%   $70.525   $70.53   $70.55   $70.50  
  Purchase #6 $15.37   5.569%   $16.226   $16.23   $16.25   $16.20  
  Purchase #7 $226.87   8.853%   $246.9548   $246.95   $246.95   $247.00  
  7 purchase totals = $826.87       $890.5368   $890.54   $890.55   $890.60