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 $55.98   11.738%   $62.5509   $62.55   $62.55   $62.60  
  Purchase #2 $87.41   8.787%   $95.0907   $95.09   $95.10   $95.10  
  Purchase #3 $190.28   9.841%   $209.0055   $209.01   $209.00   $209.00  
  Purchase #4 $157.56   5.543%   $166.2936   $166.29   $166.30   $166.30  
  Purchase #5 $126.28   3.373%   $130.5394   $130.54   $130.55   $130.50  
  Purchase #6 $210.82   6.703%   $224.9513   $224.95   $224.95   $225.00  
  Purchase #7 $77.81   6.415%   $82.8015   $82.80   $82.80   $82.80  
  7 purchase totals = $906.14       $971.2329   $971.23   $971.25   $971.30