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 $85.76   7.308%   $92.0273   $92.03   $92.05   $92.00  
  Purchase #2 $64.45   8.283%   $69.7884   $69.79   $69.80   $69.80  
  Purchase #3 $113.84   5.171%   $119.7267   $119.73   $119.75   $119.70  
  Purchase #4 $233.81   4.318%   $243.9059   $243.91   $243.90   $243.90  
  Purchase #5 $162.80   10.602%   $180.0601   $180.06   $180.05   $180.10  
  Purchase #6 $52.97   12.567%   $59.6267   $59.63   $59.65   $59.60  
  Purchase #7 $118.56   11.546%   $132.2489   $132.25   $132.25   $132.20  
  7 purchase totals = $832.19       $897.3840   $897.40   $897.45   $897.30