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 $118.98   6.832%   $127.1087   $127.11   $127.10   $127.10  
  Purchase #2 $194.37   7.855%   $209.6378   $209.64   $209.65   $209.60  
  Purchase #3 $196.52   3.786%   $203.9602   $203.96   $203.95   $204.00  
  Purchase #4 $23.92   12.130%   $26.8215   $26.82   $26.80   $26.80  
  Purchase #5 $232.95   10.393%   $257.1605   $257.16   $257.15   $257.20  
  Purchase #6 $23.99   7.749%   $25.849   $25.85   $25.85   $25.80  
  Purchase #7 $86.95   6.686%   $92.7635   $92.76   $92.75   $92.80  
  7 purchase totals = $877.68       $943.3012   $943.30   $943.25   $943.30