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 $195.96   11.549%   $218.5914   $218.59   $218.60   $218.60  
  Purchase #2 $53.55   3.711%   $55.5372   $55.54   $55.55   $55.50  
  Purchase #3 $122.64   6.586%   $130.7171   $130.72   $130.70   $130.70  
  Purchase #4 $30.91   12.698%   $34.835   $34.84   $34.85   $34.80  
  Purchase #5 $31.87   4.202%   $33.2092   $33.21   $33.20   $33.20  
  Purchase #6 $212.62   11.512%   $237.0968   $237.10   $237.10   $237.10  
  Purchase #7 $116.38   4.490%   $121.6055   $121.61   $121.60   $121.60  
  7 purchase totals = $763.93       $831.5922   $831.61   $831.60   $831.50