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 $69.92   5.487%   $73.7565   $73.76   $73.75   $73.80  
  Purchase #2 $227.39   12.184%   $255.0952   $255.10   $255.10   $255.10  
  Purchase #3 $131.72   3.241%   $135.989   $135.99   $136.00   $136.00  
  Purchase #4 $212.66   11.771%   $237.6922   $237.69   $237.70   $237.70  
  Purchase #5 $7.79   11.299%   $8.6702   $8.67   $8.65   $8.70  
  Purchase #6 $13.44   4.677%   $14.0686   $14.07   $14.05   $14.10  
  Purchase #7 $160.35   10.766%   $177.6133   $177.61   $177.60   $177.60  
  7 purchase totals = $823.27       $902.8850   $902.89   $902.85   $903.00