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 $125.97   13.256%   $142.6686   $142.67   $142.65   $142.70  
  Purchase #2 $60.70   4.566%   $63.4716   $63.47   $63.45   $63.50  
  Purchase #3 $146.74   4.807%   $153.7938   $153.79   $153.80   $153.80  
  Purchase #4 $112.27   12.805%   $126.6462   $126.65   $126.65   $126.60  
  Purchase #5 $240.55   8.770%   $261.6462   $261.65   $261.65   $261.60  
  Purchase #6 $111.67   10.621%   $123.5305   $123.53   $123.55   $123.50  
  Purchase #7 $187.41   12.442%   $210.7276   $210.73   $210.75   $210.70  
  7 purchase totals = $985.31       $1,082.4845   $1,082.49   $1,082.50   $1,082.40