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 $204.39   9.802%   $224.4243   $224.42   $224.40   $224.40  
  Purchase #2 $33.39   9.590%   $36.5921   $36.59   $36.60   $36.60  
  Purchase #3 $194.81   7.775%   $209.9565   $209.96   $209.95   $210.00  
  Purchase #4 $100.80   12.203%   $113.1006   $113.10   $113.10   $113.10  
  Purchase #5 $59.41   5.319%   $62.57   $62.57   $62.55   $62.60  
  Purchase #6 $103.97   9.122%   $113.4541   $113.45   $113.45   $113.50  
  Purchase #7 $7.34   8.287%   $7.9483   $7.95   $7.95   $7.90  
  7 purchase totals = $704.11       $768.0459   $768.04   $768.00   $768.10