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 $245.89   11.247%   $273.5452   $273.55   $273.55   $273.50  
  Purchase #2 $94.71   8.438%   $102.7016   $102.70   $102.70   $102.70  
  Purchase #3 $91.45   4.299%   $95.3814   $95.38   $95.40   $95.40  
  Purchase #4 $188.35   12.661%   $212.197   $212.20   $212.20   $212.20  
  Purchase #5 $178.85   4.201%   $186.3635   $186.36   $186.35   $186.40  
  Purchase #6 $26.25   8.140%   $28.3868   $28.39   $28.40   $28.40  
  Purchase #7 $243.57   11.434%   $271.4198   $271.42   $271.40   $271.40  
  7 purchase totals = $1,069.07       $1,169.9953   $1,170.00   $1,170.00   $1,170.00