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 $246.97   13.471%   $280.2393   $280.24   $280.25   $280.20  
  Purchase #2 $179.46   5.650%   $189.5995   $189.60   $189.60   $189.60  
  Purchase #3 $15.71   13.280%   $17.7963   $17.80   $17.80   $17.80  
  Purchase #4 $83.43   13.861%   $94.9942   $94.99   $95.00   $95.00  
  Purchase #5 $211.47   6.212%   $224.6065   $224.61   $224.60   $224.60  
  Purchase #6 $5.50   8.379%   $5.9608   $5.96   $5.95   $6.00  
  Purchase #7 $176.35   13.403%   $199.9862   $199.99   $200.00   $200.00  
  7 purchase totals = $918.89       $1,013.1828   $1,013.19   $1,013.20   $1,013.20