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 $83.82   10.431%   $92.5633   $92.56   $92.55   $92.60  
  Purchase #2 $196.32   12.412%   $220.6872   $220.69   $220.70   $220.70  
  Purchase #3 $237.83   9.208%   $259.7294   $259.73   $259.75   $259.70  
  Purchase #4 $66.49   4.541%   $69.5093   $69.51   $69.50   $69.50  
  Purchase #5 $31.34   9.386%   $34.2816   $34.28   $34.30   $34.30  
  Purchase #6 $93.32   11.261%   $103.8288   $103.83   $103.85   $103.80  
  Purchase #7 $184.50   8.468%   $200.1235   $200.12   $200.10   $200.10  
  7 purchase totals = $893.62       $980.7231   $980.72   $980.75   $980.70