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 $241.63   7.398%   $259.5058   $259.51   $259.50   $259.50  
  Purchase #2 $65.87   7.409%   $70.7503   $70.75   $70.75   $70.80  
  Purchase #3 $153.30   9.844%   $168.3909   $168.39   $168.40   $168.40  
  Purchase #4 $194.25   11.233%   $216.0701   $216.07   $216.05   $216.10  
  Purchase #5 $175.63   5.145%   $184.6662   $184.67   $184.65   $184.70  
  Purchase #6 $151.74   7.254%   $162.7472   $162.75   $162.75   $162.70  
  Purchase #7 $30.37   3.183%   $31.3367   $31.34   $31.35   $31.30  
  7 purchase totals = $1,012.79       $1,093.4672   $1,093.48   $1,093.45   $1,093.50