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 $22.72   9.155%   $24.8   $24.80   $24.80   $24.80  
  Purchase #2 $66.62   13.474%   $75.5964   $75.60   $75.60   $75.60  
  Purchase #3 $52.26   3.692%   $54.1894   $54.19   $54.20   $54.20  
  Purchase #4 $180.85   7.256%   $193.9725   $193.97   $193.95   $194.00  
  Purchase #5 $92.79   11.677%   $103.6251   $103.63   $103.65   $103.60  
  Purchase #6 $49.32   3.441%   $51.0171   $51.02   $51.00   $51.00  
  Purchase #7 $112.97   10.132%   $124.4161   $124.42   $124.40   $124.40  
  7 purchase totals = $577.53       $627.6166   $627.63   $627.60   $627.60