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 $194.58   8.744%   $211.5941   $211.59   $211.60   $211.60  
  Purchase #2 $116.68   12.789%   $131.6022   $131.60   $131.60   $131.60  
  Purchase #3 $26.86   6.824%   $28.6929   $28.69   $28.70   $28.70  
  Purchase #4 $51.66   4.462%   $53.9651   $53.97   $53.95   $54.00  
  Purchase #5 $152.46   5.573%   $160.9566   $160.96   $160.95   $161.00  
  Purchase #6 $225.82   5.725%   $238.7482   $238.75   $238.75   $238.70  
  Purchase #7 $116.33   9.123%   $126.9428   $126.94   $126.95   $126.90  
  7 purchase totals = $884.39       $952.5019   $952.50   $952.50   $952.50