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 $29.48   11.446%   $32.8543   $32.85   $32.85   $32.90  
  Purchase #2 $228.83   3.692%   $237.2784   $237.28   $237.30   $237.30  
  Purchase #3 $164.89   6.768%   $176.0498   $176.05   $176.05   $176.00  
  Purchase #4 $15.82   10.612%   $17.4988   $17.50   $17.50   $17.50  
  Purchase #5 $63.79   4.342%   $66.5598   $66.56   $66.55   $66.60  
  Purchase #6 $55.86   3.181%   $57.6369   $57.64   $57.65   $57.60  
  Purchase #7 $148.52   8.141%   $160.611   $160.61   $160.60   $160.60  
  7 purchase totals = $707.19       $748.4890   $748.49   $748.50   $748.50