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 $155.76   12.699%   $175.54   $175.54   $175.55   $175.50  
  Purchase #2 $87.43   12.631%   $98.4733   $98.47   $98.45   $98.50  
  Purchase #3 $239.97   12.688%   $270.4174   $270.42   $270.40   $270.40  
  Purchase #4 $62.42   5.225%   $65.6814   $65.68   $65.70   $65.70  
  Purchase #5 $191.26   10.202%   $210.7723   $210.77   $210.75   $210.80  
  Purchase #6 $172.65   9.874%   $189.6975   $189.70   $189.70   $189.70  
  Purchase #7 $153.82   8.390%   $166.7255   $166.73   $166.75   $166.70  
  7 purchase totals = $1,063.31       $1,177.3074   $1,177.31   $1,177.30   $1,177.30