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 $82.53   13.191%   $93.4165   $93.42   $93.40   $93.40  
  Purchase #2 $146.92   5.117%   $154.4379   $154.44   $154.45   $154.40  
  Purchase #3 $210.61   6.676%   $224.6703   $224.67   $224.65   $224.70  
  Purchase #4 $236.99   11.613%   $264.5116   $264.51   $264.50   $264.50  
  Purchase #5 $166.51   3.204%   $171.845   $171.85   $171.85   $171.80  
  Purchase #6 $216.76   8.540%   $235.2713   $235.27   $235.25   $235.30  
  Purchase #7 $155.64   12.861%   $175.6569   $175.66   $175.65   $175.70  
  7 purchase totals = $1,215.96       $1,319.8095   $1,319.82   $1,319.75   $1,319.80