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 $241.30   10.681%   $267.0733   $267.07   $267.05   $267.10  
  Purchase #2 $55.71   6.788%   $59.4916   $59.49   $59.50   $59.50  
  Purchase #3 $217.77   7.863%   $234.8933   $234.89   $234.90   $234.90  
  Purchase #4 $196.98   4.469%   $205.783   $205.78   $205.80   $205.80  
  Purchase #5 $12.71   11.623%   $14.1873   $14.19   $14.20   $14.20  
  Purchase #6 $134.78   3.272%   $139.19   $139.19   $139.20   $139.20  
  Purchase #7 $188.71   12.169%   $211.6741   $211.67   $211.65   $211.70  
  7 purchase totals = $1,047.96       $1,132.2926   $1,132.28   $1,132.30   $1,132.40