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 $53.76   10.268%   $59.2801   $59.28   $59.30   $59.30  
  Purchase #2 $212.51   5.418%   $224.0238   $224.02   $224.00   $224.00  
  Purchase #3 $198.69   7.824%   $214.2355   $214.24   $214.25   $214.20  
  Purchase #4 $225.47   9.188%   $246.1862   $246.19   $246.20   $246.20  
  Purchase #5 $121.84   6.567%   $129.8412   $129.84   $129.85   $129.80  
  Purchase #6 $194.83   11.798%   $217.816   $217.82   $217.80   $217.80  
  Purchase #7 $79.88   5.291%   $84.1065   $84.11   $84.10   $84.10  
  7 purchase totals = $1,086.98       $1,175.4893   $1,175.50   $1,175.50   $1,175.40