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 $76.81   8.457%   $83.3058   $83.31   $83.30   $83.30  
  Purchase #2 $59.49   7.808%   $64.135   $64.14   $64.15   $64.10  
  Purchase #3 $163.57   4.455%   $170.857   $170.86   $170.85   $170.90  
  Purchase #4 $78.41   7.575%   $84.3496   $84.35   $84.35   $84.30  
  Purchase #5 $158.26   8.480%   $171.6804   $171.68   $171.70   $171.70  
  Purchase #6 $185.77   7.656%   $199.9926   $199.99   $200.00   $200.00  
  Purchase #7 $224.48   6.459%   $238.9792   $238.98   $239.00   $239.00  
  7 purchase totals = $946.79       $1,013.2996   $1,013.31   $1,013.35   $1,013.30