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 $62.88   8.230%   $68.055   $68.06   $68.05   $68.10  
  Purchase #2 $211.96   8.804%   $230.621   $230.62   $230.60   $230.60  
  Purchase #3 $246.82   13.319%   $279.694   $279.69   $279.70   $279.70  
  Purchase #4 $156.34   9.499%   $171.1907   $171.19   $171.20   $171.20  
  Purchase #5 $58.89   9.294%   $64.3632   $64.36   $64.35   $64.40  
  Purchase #6 $59.72   10.872%   $66.2128   $66.21   $66.20   $66.20  
  Purchase #7 $92.39   11.438%   $102.9576   $102.96   $102.95   $103.00  
  7 purchase totals = $889.00       $983.0943   $983.09   $983.05   $983.20