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 $238.45   10.719%   $264.0095   $264.01   $264.00   $264.00  
  Purchase #2 $146.94   8.463%   $159.3755   $159.38   $159.40   $159.40  
  Purchase #3 $157.99   10.243%   $174.1729   $174.17   $174.15   $174.20  
  Purchase #4 $96.69   8.152%   $104.5722   $104.57   $104.55   $104.60  
  Purchase #5 $90.35   3.183%   $93.2258   $93.23   $93.25   $93.20  
  Purchase #6 $69.93   7.154%   $74.9328   $74.93   $74.95   $74.90  
  Purchase #7 $54.64   11.585%   $60.97   $60.97   $60.95   $61.00  
  7 purchase totals = $854.99       $931.2587   $931.26   $931.25   $931.30