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 $242.59   12.619%   $273.2024   $273.20   $273.20   $273.20  
  Purchase #2 $67.73   12.341%   $76.0886   $76.09   $76.10   $76.10  
  Purchase #3 $110.78   7.763%   $119.3799   $119.38   $119.40   $119.40  
  Purchase #4 $80.46   6.561%   $85.739   $85.74   $85.75   $85.70  
  Purchase #5 $171.49   11.508%   $191.2251   $191.23   $191.25   $191.20  
  Purchase #6 $131.85   11.359%   $146.8268   $146.83   $146.85   $146.80  
  Purchase #7 $187.58   9.245%   $204.9218   $204.92   $204.90   $204.90  
  7 purchase totals = $992.48       $1,097.3836   $1,097.39   $1,097.45   $1,097.30