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 $132.80   11.199%   $147.6723   $147.67   $147.65   $147.70  
  Purchase #2 $191.77   13.434%   $217.5324   $217.53   $217.55   $217.50  
  Purchase #3 $118.95   10.873%   $131.8834   $131.88   $131.90   $131.90  
  Purchase #4 $227.43   10.324%   $250.9099   $250.91   $250.90   $250.90  
  Purchase #5 $133.36   3.788%   $138.4117   $138.41   $138.40   $138.40  
  Purchase #6 $69.47   12.210%   $77.9523   $77.95   $77.95   $78.00  
  Purchase #7 $214.92   12.820%   $242.4727   $242.47   $242.45   $242.50  
  7 purchase totals = $1,088.70       $1,206.8347   $1,206.82   $1,206.80   $1,206.90