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 $41.95   12.180%   $47.0595   $47.06   $47.05   $47.10  
  Purchase #2 $134.68   6.752%   $143.7736   $143.77   $143.75   $143.80  
  Purchase #3 $123.89   7.341%   $132.9848   $132.98   $133.00   $133.00  
  Purchase #4 $159.47   7.795%   $171.9007   $171.90   $171.90   $171.90  
  Purchase #5 $246.25   10.327%   $271.6802   $271.68   $271.70   $271.70  
  Purchase #6 $17.80   6.811%   $19.0124   $19.01   $19.00   $19.00  
  Purchase #7 $156.37   5.530%   $165.0173   $165.02   $165.00   $165.00  
  7 purchase totals = $880.41       $951.4285   $951.42   $951.40   $951.50