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 $56.61   10.208%   $62.3887   $62.39   $62.40   $62.40  
  Purchase #2 $241.79   5.867%   $255.9758   $255.98   $256.00   $256.00  
  Purchase #3 $196.62   11.858%   $219.9352   $219.94   $219.95   $219.90  
  Purchase #4 $180.90   10.307%   $199.5454   $199.55   $199.55   $199.50  
  Purchase #5 $210.91   13.546%   $239.4799   $239.48   $239.50   $239.50  
  Purchase #6 $212.49   9.166%   $231.9668   $231.97   $231.95   $232.00  
  Purchase #7 $69.89   9.368%   $76.4373   $76.44   $76.45   $76.40  
  7 purchase totals = $1,169.21       $1,285.7291   $1,285.75   $1,285.80   $1,285.70