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 $235.59   7.219%   $252.5972   $252.60   $252.60   $252.60  
  Purchase #2 $48.73   10.587%   $53.889   $53.89   $53.90   $53.90  
  Purchase #3 $44.73   6.483%   $47.6298   $47.63   $47.65   $47.60  
  Purchase #4 $144.89   7.651%   $155.9755   $155.98   $156.00   $156.00  
  Purchase #5 $117.42   3.796%   $121.8773   $121.88   $121.90   $121.90  
  Purchase #6 $25.25   4.165%   $26.3017   $26.30   $26.30   $26.30  
  Purchase #7 $92.51   13.511%   $105.009   $105.01   $105.00   $105.00  
  7 purchase totals = $709.12       $763.2795   $763.29   $763.35   $763.30