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 $126.52   5.834%   $133.9012   $133.90   $133.90   $133.90  
  Purchase #2 $223.98   13.185%   $253.5118   $253.51   $253.50   $253.50  
  Purchase #3 $169.95   7.453%   $182.6164   $182.62   $182.60   $182.60  
  Purchase #4 $234.56   7.560%   $252.2927   $252.29   $252.30   $252.30  
  Purchase #5 $28.91   5.826%   $30.5943   $30.59   $30.60   $30.60  
  Purchase #6 $230.72   11.167%   $256.4845   $256.48   $256.50   $256.50  
  Purchase #7 $144.68   13.776%   $164.6111   $164.61   $164.60   $164.60  
  7 purchase totals = $1,159.32       $1,274.0120   $1,274.00   $1,274.00   $1,274.00