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 $241.25   11.841%   $269.8164   $269.82   $269.80   $269.80  
  Purchase #2 $233.35   6.835%   $249.2995   $249.30   $249.30   $249.30  
  Purchase #3 $218.53   3.301%   $225.7437   $225.74   $225.75   $225.70  
  Purchase #4 $19.83   7.298%   $21.2772   $21.28   $21.30   $21.30  
  Purchase #5 $35.54   5.160%   $37.3739   $37.37   $37.35   $37.40  
  Purchase #6 $46.65   5.269%   $49.108   $49.11   $49.10   $49.10  
  Purchase #7 $28.68   7.191%   $30.7424   $30.74   $30.75   $30.70  
  7 purchase totals = $823.83       $883.3611   $883.36   $883.35   $883.30