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 $216.59   11.727%   $241.9895   $241.99   $242.00   $242.00  
  Purchase #2 $241.82   11.415%   $269.4238   $269.42   $269.40   $269.40  
  Purchase #3 $170.43   10.778%   $188.7989   $188.80   $188.80   $188.80  
  Purchase #4 $14.51   6.682%   $15.4796   $15.48   $15.50   $15.50  
  Purchase #5 $197.49   9.191%   $215.6413   $215.64   $215.65   $215.60  
  Purchase #6 $40.48   10.342%   $44.6664   $44.67   $44.65   $44.70  
  Purchase #7 $59.26   6.794%   $63.2861   $63.29   $63.30   $63.30  
  7 purchase totals = $940.58       $1,039.2856   $1,039.29   $1,039.30   $1,039.30