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 $191.72   6.508%   $204.1971   $204.20   $204.20   $204.20  
  Purchase #2 $203.91   11.409%   $227.1741   $227.17   $227.15   $227.20  
  Purchase #3 $119.30   13.642%   $135.5749   $135.57   $135.55   $135.60  
  Purchase #4 $62.59   5.548%   $66.0625   $66.06   $66.05   $66.10  
  Purchase #5 $158.42   3.839%   $164.5017   $164.50   $164.50   $164.50  
  Purchase #6 $60.71   12.172%   $68.0996   $68.10   $68.10   $68.10  
  Purchase #7 $10.97   11.855%   $12.2705   $12.27   $12.25   $12.30  
  7 purchase totals = $807.62       $877.8804   $877.87   $877.80   $878.00