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 $87.27   9.760%   $95.7876   $95.79   $95.80   $95.80  
  Purchase #2 $53.32   7.310%   $57.2177   $57.22   $57.20   $57.20  
  Purchase #3 $118.97   9.692%   $130.5006   $130.50   $130.50   $130.50  
  Purchase #4 $128.38   7.266%   $137.7081   $137.71   $137.70   $137.70  
  Purchase #5 $246.35   6.552%   $262.4909   $262.49   $262.50   $262.50  
  Purchase #6 $180.28   7.548%   $193.8875   $193.89   $193.90   $193.90  
  Purchase #7 $58.30   5.313%   $61.3975   $61.40   $61.40   $61.40  
  7 purchase totals = $872.87       $938.9899   $939.00   $939.00   $939.00