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 $226.74   8.582%   $246.1988   $246.20   $246.20   $246.20  
  Purchase #2 $68.50   7.327%   $73.519   $73.52   $73.50   $73.50  
  Purchase #3 $161.26   6.231%   $171.3081   $171.31   $171.30   $171.30  
  Purchase #4 $203.60   10.581%   $225.1429   $225.14   $225.15   $225.10  
  Purchase #5 $62.85   11.708%   $70.2085   $70.21   $70.20   $70.20  
  Purchase #6 $98.58   13.637%   $112.0234   $112.02   $112.00   $112.00  
  Purchase #7 $70.55   7.688%   $75.9739   $75.97   $75.95   $76.00  
  7 purchase totals = $892.08       $974.3746   $974.37   $974.30   $974.30