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 $110.93   13.819%   $126.2594   $126.26   $126.25   $126.30  
  Purchase #2 $149.78   6.713%   $159.8347   $159.83   $159.85   $159.80  
  Purchase #3 $42.27   12.151%   $47.4062   $47.41   $47.40   $47.40  
  Purchase #4 $199.41   10.767%   $220.8805   $220.88   $220.90   $220.90  
  Purchase #5 $194.39   7.706%   $209.3697   $209.37   $209.35   $209.40  
  Purchase #6 $78.78   7.787%   $84.9146   $84.91   $84.90   $84.90  
  Purchase #7 $123.98   11.285%   $137.9711   $137.97   $137.95   $138.00  
  7 purchase totals = $899.54       $986.6362   $986.63   $986.60   $986.70