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 $206.49   8.791%   $224.6425   $224.64   $224.65   $224.60  
  Purchase #2 $178.75   10.750%   $197.9656   $197.97   $197.95   $198.00  
  Purchase #3 $124.41   13.746%   $141.5114   $141.51   $141.50   $141.50  
  Purchase #4 $105.95   7.191%   $113.5689   $113.57   $113.55   $113.60  
  Purchase #5 $214.98   13.382%   $243.7486   $243.75   $243.75   $243.70  
  Purchase #6 $85.33   7.127%   $91.4115   $91.41   $91.40   $91.40  
  Purchase #7 $92.36   3.681%   $95.7598   $95.76   $95.75   $95.80  
  7 purchase totals = $1,008.27       $1,108.6083   $1,108.61   $1,108.55   $1,108.60