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 $241.25   12.508%   $271.4256   $271.43   $271.45   $271.40  
  Purchase #2 $136.61   3.217%   $141.0047   $141.00   $141.00   $141.00  
  Purchase #3 $171.44   11.607%   $191.339   $191.34   $191.35   $191.30  
  Purchase #4 $68.98   10.118%   $75.9594   $75.96   $75.95   $76.00  
  Purchase #5 $66.60   3.802%   $69.1321   $69.13   $69.15   $69.10  
  Purchase #6 $60.65   10.688%   $67.1323   $67.13   $67.15   $67.10  
  Purchase #7 $59.65   13.798%   $67.8805   $67.88   $67.90   $67.90  
  7 purchase totals = $805.18       $883.8736   $883.87   $883.95   $883.80