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 $56.38   7.494%   $60.6051   $60.61   $60.60   $60.60  
  Purchase #2 $32.30   7.243%   $34.6395   $34.64   $34.65   $34.60  
  Purchase #3 $60.68   9.694%   $66.5623   $66.56   $66.55   $66.60  
  Purchase #4 $92.93   5.306%   $97.8609   $97.86   $97.85   $97.90  
  Purchase #5 $60.78   9.347%   $66.4611   $66.46   $66.45   $66.50  
  Purchase #6 $116.81   6.742%   $124.6853   $124.69   $124.70   $124.70  
  Purchase #7 $63.59   9.761%   $69.797   $69.80   $69.80   $69.80  
  7 purchase totals = $483.47       $520.6112   $520.62   $520.60   $520.70