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 $227.60   8.105%   $246.047   $246.05   $246.05   $246.00  
  Purchase #2 $229.84   5.265%   $241.9411   $241.94   $241.95   $241.90  
  Purchase #3 $102.67   7.512%   $110.3826   $110.38   $110.40   $110.40  
  Purchase #4 $61.87   7.262%   $66.363   $66.36   $66.35   $66.40  
  Purchase #5 $210.46   3.270%   $217.342   $217.34   $217.35   $217.30  
  Purchase #6 $79.94   7.441%   $85.8883   $85.89   $85.90   $85.90  
  Purchase #7 $93.71   9.310%   $102.4344   $102.43   $102.45   $102.40  
  7 purchase totals = $1,006.09       $1,070.3984   $1,070.39   $1,070.45   $1,070.30