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 $58.55   9.145%   $63.9044   $63.90   $63.90   $63.90  
  Purchase #2 $226.60   12.785%   $255.5708   $255.57   $255.55   $255.60  
  Purchase #3 $244.51   9.178%   $266.9511   $266.95   $266.95   $267.00  
  Purchase #4 $197.73   3.224%   $204.1048   $204.10   $204.10   $204.10  
  Purchase #5 $51.72   12.411%   $58.139   $58.14   $58.15   $58.10  
  Purchase #6 $7.27   8.524%   $7.8897   $7.89   $7.90   $7.90  
  Purchase #7 $61.79   10.552%   $68.3101   $68.31   $68.30   $68.30  
  7 purchase totals = $848.17       $924.8699   $924.86   $924.85   $924.90