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 $84.69   9.126%   $92.4188   $92.42   $92.40   $92.40  
  Purchase #2 $218.90   10.417%   $241.7028   $241.70   $241.70   $241.70  
  Purchase #3 $204.68   9.298%   $223.7111   $223.71   $223.70   $223.70  
  Purchase #4 $90.68   4.637%   $94.8848   $94.88   $94.90   $94.90  
  Purchase #5 $121.32   7.471%   $130.3838   $130.38   $130.40   $130.40  
  Purchase #6 $86.93   12.417%   $97.7241   $97.72   $97.70   $97.70  
  Purchase #7 $65.46   9.848%   $71.9065   $71.91   $71.90   $71.90  
  7 purchase totals = $872.66       $952.7319   $952.72   $952.70   $952.70