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 $117.87   9.457%   $129.017   $129.02   $129.00   $129.00  
  Purchase #2 $160.42   10.348%   $177.0203   $177.02   $177.00   $177.00  
  Purchase #3 $113.73   3.548%   $117.7651   $117.77   $117.75   $117.80  
  Purchase #4 $206.43   7.781%   $222.4923   $222.49   $222.50   $222.50  
  Purchase #5 $164.88   5.281%   $173.5873   $173.59   $173.60   $173.60  
  Purchase #6 $12.44   7.742%   $13.4031   $13.40   $13.40   $13.40  
  Purchase #7 $177.62   9.204%   $193.9681   $193.97   $193.95   $194.00  
  7 purchase totals = $953.39       $1,027.2532   $1,027.26   $1,027.20   $1,027.30