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 $61.74   4.210%   $64.3393   $64.34   $64.35   $64.30  
  Purchase #2 $190.43   10.497%   $210.4194   $210.42   $210.40   $210.40  
  Purchase #3 $53.44   11.631%   $59.6556   $59.66   $59.65   $59.70  
  Purchase #4 $146.87   10.844%   $162.7966   $162.80   $162.80   $162.80  
  Purchase #5 $102.39   13.537%   $116.2505   $116.25   $116.25   $116.30  
  Purchase #6 $170.66   6.828%   $182.3127   $182.31   $182.30   $182.30  
  Purchase #7 $240.86   6.746%   $257.1084   $257.11   $257.10   $257.10  
  7 purchase totals = $966.39       $1,052.8825   $1,052.89   $1,052.85   $1,052.90