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 $191.32   9.187%   $208.8966   $208.90   $208.90   $208.90  
  Purchase #2 $148.87   13.338%   $168.7263   $168.73   $168.75   $168.70  
  Purchase #3 $223.56   4.766%   $234.2149   $234.21   $234.20   $234.20  
  Purchase #4 $112.26   8.409%   $121.6999   $121.70   $121.70   $121.70  
  Purchase #5 $243.41   13.407%   $276.044   $276.04   $276.05   $276.00  
  Purchase #6 $157.96   4.762%   $165.4821   $165.48   $165.50   $165.50  
  Purchase #7 $87.75   13.604%   $99.6875   $99.69   $99.70   $99.70  
  7 purchase totals = $1,165.13       $1,274.7513   $1,274.75   $1,274.80   $1,274.70