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 $52.84   4.617%   $55.2796   $55.28   $55.30   $55.30  
  Purchase #2 $156.69   10.684%   $173.4308   $173.43   $173.45   $173.40  
  Purchase #3 $106.34   9.712%   $116.6677   $116.67   $116.65   $116.70  
  Purchase #4 $204.66   11.418%   $228.0281   $228.03   $228.05   $228.00  
  Purchase #5 $69.89   4.872%   $73.295   $73.30   $73.30   $73.30  
  Purchase #6 $240.26   5.643%   $253.8179   $253.82   $253.80   $253.80  
  Purchase #7 $104.96   7.619%   $112.9569   $112.96   $112.95   $113.00  
  7 purchase totals = $935.64       $1,013.4760   $1,013.49   $1,013.50   $1,013.50