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 $244.78   12.252%   $274.7704   $274.77   $274.75   $274.80  
  Purchase #2 $239.63   8.230%   $259.3515   $259.35   $259.35   $259.40  
  Purchase #3 $71.70   4.624%   $75.0154   $75.02   $75.00   $75.00  
  Purchase #4 $241.87   13.690%   $274.982   $274.98   $275.00   $275.00  
  Purchase #5 $156.56   10.589%   $173.1381   $173.14   $173.15   $173.10  
  Purchase #6 $14.31   9.754%   $15.7058   $15.71   $15.70   $15.70  
  Purchase #7 $55.89   4.831%   $58.59   $58.59   $58.60   $58.60  
  7 purchase totals = $1,024.74       $1,131.5532   $1,131.56   $1,131.55   $1,131.60