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 $59.58   5.598%   $62.9153   $62.92   $62.90   $62.90  
  Purchase #2 $68.69   12.201%   $77.0709   $77.07   $77.05   $77.10  
  Purchase #3 $193.86   10.460%   $214.1378   $214.14   $214.15   $214.10  
  Purchase #4 $110.88   11.573%   $123.7121   $123.71   $123.70   $123.70  
  Purchase #5 $245.35   7.397%   $263.4985   $263.50   $263.50   $263.50  
  Purchase #6 $136.45   8.500%   $148.0483   $148.05   $148.05   $148.00  
  Purchase #7 $26.78   9.474%   $29.3171   $29.32   $29.30   $29.30  
  7 purchase totals = $841.59       $918.7000   $918.71   $918.65   $918.60