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 $229.57   7.203%   $246.1059   $246.11   $246.10   $246.10  
  Purchase #2 $102.77   13.183%   $116.3182   $116.32   $116.30   $116.30  
  Purchase #3 $170.89   3.779%   $177.3479   $177.35   $177.35   $177.30  
  Purchase #4 $47.34   4.781%   $49.6033   $49.60   $49.60   $49.60  
  Purchase #5 $151.56   5.302%   $159.5957   $159.60   $159.60   $159.60  
  Purchase #6 $166.61   11.592%   $185.9234   $185.92   $185.90   $185.90  
  Purchase #7 $114.27   5.779%   $120.8737   $120.87   $120.85   $120.90  
  7 purchase totals = $983.01       $1,055.7681   $1,055.77   $1,055.70   $1,055.70