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 $243.98   6.854%   $260.7024   $260.70   $260.70   $260.70  
  Purchase #2 $246.34   11.310%   $274.2011   $274.20   $274.20   $274.20  
  Purchase #3 $65.36   6.816%   $69.8149   $69.81   $69.80   $69.80  
  Purchase #4 $78.81   6.406%   $83.8586   $83.86   $83.85   $83.90  
  Purchase #5 $189.69   9.535%   $207.7769   $207.78   $207.80   $207.80  
  Purchase #6 $156.57   5.657%   $165.4272   $165.43   $165.45   $165.40  
  Purchase #7 $133.27   4.618%   $139.4244   $139.42   $139.40   $139.40  
  7 purchase totals = $1,114.02       $1,201.2055   $1,201.20   $1,201.20   $1,201.20