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 $120.76   11.549%   $134.7066   $134.71   $134.70   $134.70  
  Purchase #2 $78.59   4.756%   $82.3277   $82.33   $82.35   $82.30  
  Purchase #3 $248.39   4.817%   $260.3549   $260.35   $260.35   $260.40  
  Purchase #4 $115.26   5.657%   $121.7803   $121.78   $121.80   $121.80  
  Purchase #5 $120.42   8.458%   $130.6051   $130.61   $130.60   $130.60  
  Purchase #6 $213.77   5.783%   $226.1323   $226.13   $226.15   $226.10  
  Purchase #7 $82.54   6.348%   $87.7796   $87.78   $87.80   $87.80  
  7 purchase totals = $979.73       $1,043.6865   $1,043.69   $1,043.75   $1,043.70