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 $116.52   8.599%   $126.5396   $126.54   $126.55   $126.50  
  Purchase #2 $23.72   10.358%   $26.1769   $26.18   $26.20   $26.20  
  Purchase #3 $44.44   6.793%   $47.4588   $47.46   $47.45   $47.50  
  Purchase #4 $85.34   3.805%   $88.5872   $88.59   $88.60   $88.60  
  Purchase #5 $173.82   6.280%   $184.7359   $184.74   $184.75   $184.70  
  Purchase #6 $224.57   13.535%   $254.9655   $254.97   $254.95   $255.00  
  Purchase #7 $207.63   4.853%   $217.7063   $217.71   $217.70   $217.70  
  7 purchase totals = $876.04       $946.1702   $946.19   $946.20   $946.20