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 $249.68   7.661%   $268.808   $268.81   $268.80   $268.80  
  Purchase #2 $192.88   13.290%   $218.5138   $218.51   $218.50   $218.50  
  Purchase #3 $73.70   10.745%   $81.6191   $81.62   $81.60   $81.60  
  Purchase #4 $99.97   7.773%   $107.7407   $107.74   $107.75   $107.70  
  Purchase #5 $185.56   3.268%   $191.6241   $191.62   $191.60   $191.60  
  Purchase #6 $135.58   3.842%   $140.789   $140.79   $140.80   $140.80  
  Purchase #7 $48.58   5.374%   $51.1907   $51.19   $51.20   $51.20  
  7 purchase totals = $985.95       $1,060.2854   $1,060.28   $1,060.25   $1,060.20