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 $14.33   12.473%   $16.1174   $16.12   $16.10   $16.10  
  Purchase #2 $127.76   10.639%   $141.3524   $141.35   $141.35   $141.40  
  Purchase #3 $75.26   11.451%   $83.878   $83.88   $83.90   $83.90  
  Purchase #4 $184.49   10.331%   $203.5497   $203.55   $203.55   $203.50  
  Purchase #5 $104.54   12.568%   $117.6786   $117.68   $117.70   $117.70  
  Purchase #6 $187.48   6.292%   $199.2762   $199.28   $199.30   $199.30  
  Purchase #7 $163.94   5.430%   $172.8419   $172.84   $172.85   $172.80  
  7 purchase totals = $857.80       $934.6942   $934.70   $934.75   $934.70