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 $68.76   11.825%   $76.8909   $76.89   $76.90   $76.90  
  Purchase #2 $14.29   8.324%   $15.4795   $15.48   $15.50   $15.50  
  Purchase #3 $241.72   6.323%   $257.004   $257.00   $257.00   $257.00  
  Purchase #4 $28.54   11.742%   $31.8912   $31.89   $31.90   $31.90  
  Purchase #5 $240.35   10.781%   $266.2621   $266.26   $266.25   $266.30  
  Purchase #6 $36.54   12.223%   $41.0063   $41.01   $41.00   $41.00  
  Purchase #7 $246.93   7.697%   $265.9362   $265.94   $265.95   $265.90  
  7 purchase totals = $877.13       $954.4702   $954.47   $954.50   $954.50