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 $195.96   10.736%   $216.9983   $217.00   $217.00   $217.00  
  Purchase #2 $143.71   6.227%   $152.6588   $152.66   $152.65   $152.70  
  Purchase #3 $11.93   3.631%   $12.3632   $12.36   $12.35   $12.40  
  Purchase #4 $103.74   8.354%   $112.4064   $112.41   $112.40   $112.40  
  Purchase #5 $227.86   11.536%   $254.1459   $254.15   $254.15   $254.10  
  Purchase #6 $74.45   13.428%   $84.4471   $84.45   $84.45   $84.40  
  Purchase #7 $168.93   3.751%   $175.2666   $175.27   $175.25   $175.30  
  7 purchase totals = $926.58       $1,008.2863   $1,008.30   $1,008.25   $1,008.30