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 $41.76   13.412%   $47.3609   $47.36   $47.35   $47.40  
  Purchase #2 $250.59   10.417%   $276.694   $276.69   $276.70   $276.70  
  Purchase #3 $16.95   4.747%   $17.7546   $17.75   $17.75   $17.80  
  Purchase #4 $155.35   8.206%   $168.098   $168.10   $168.10   $168.10  
  Purchase #5 $22.86   11.478%   $25.4839   $25.48   $25.50   $25.50  
  Purchase #6 $67.77   3.143%   $69.9   $69.90   $69.90   $69.90  
  Purchase #7 $166.59   8.121%   $180.1188   $180.12   $180.10   $180.10  
  7 purchase totals = $721.87       $785.4102   $785.40   $785.40   $785.50