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 $214.61   8.107%   $232.0084   $232.01   $232.00   $232.00  
  Purchase #2 $188.72   11.619%   $210.6474   $210.65   $210.65   $210.60  
  Purchase #3 $91.70   13.602%   $104.173   $104.17   $104.15   $104.20  
  Purchase #4 $63.67   12.801%   $71.8204   $71.82   $71.80   $71.80  
  Purchase #5 $148.68   4.660%   $155.6085   $155.61   $155.60   $155.60  
  Purchase #6 $113.38   9.755%   $124.4402   $124.44   $124.45   $124.40  
  Purchase #7 $113.65   9.260%   $124.174   $124.17   $124.15   $124.20  
  7 purchase totals = $934.41       $1,022.8719   $1,022.87   $1,022.80   $1,022.80