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 $55.69   13.617%   $63.2733   $63.27   $63.25   $63.30  
  Purchase #2 $217.85   8.176%   $235.6614   $235.66   $235.65   $235.70  
  Purchase #3 $90.29   4.260%   $94.1364   $94.14   $94.15   $94.10  
  Purchase #4 $28.93   5.217%   $30.4393   $30.44   $30.45   $30.40  
  Purchase #5 $157.49   8.307%   $170.5727   $170.57   $170.55   $170.60  
  Purchase #6 $211.44   6.473%   $225.1265   $225.13   $225.15   $225.10  
  Purchase #7 $62.94   3.753%   $65.3021   $65.30   $65.30   $65.30  
  7 purchase totals = $824.63       $884.5117   $884.51   $884.50   $884.50