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 $95.62   10.817%   $105.9632   $105.96   $105.95   $106.00  
  Purchase #2 $114.49   7.647%   $123.2451   $123.25   $123.25   $123.20  
  Purchase #3 $160.93   9.872%   $176.817   $176.82   $176.80   $176.80  
  Purchase #4 $194.54   11.117%   $216.167   $216.17   $216.15   $216.20  
  Purchase #5 $11.65   9.238%   $12.7262   $12.73   $12.75   $12.70  
  Purchase #6 $92.75   5.515%   $97.8652   $97.87   $97.85   $97.90  
  Purchase #7 $102.89   13.187%   $116.4581   $116.46   $116.45   $116.50  
  7 purchase totals = $772.87       $849.2418   $849.26   $849.20   $849.30