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 $64.43   8.543%   $69.9343   $69.93   $69.95   $69.90  
  Purchase #2 $61.50   11.471%   $68.5547   $68.55   $68.55   $68.60  
  Purchase #3 $233.63   7.852%   $251.9746   $251.97   $251.95   $252.00  
  Purchase #4 $193.51   6.676%   $206.4287   $206.43   $206.45   $206.40  
  Purchase #5 $101.88   3.497%   $105.4427   $105.44   $105.45   $105.40  
  Purchase #6 $219.54   9.273%   $239.8979   $239.90   $239.90   $239.90  
  Purchase #7 $22.38   11.840%   $25.0298   $25.03   $25.05   $25.00  
  7 purchase totals = $896.87       $967.2627   $967.25   $967.30   $967.20