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 $110.98   4.758%   $116.2604   $116.26   $116.25   $116.30  
  Purchase #2 $185.33   9.648%   $203.2106   $203.21   $203.20   $203.20  
  Purchase #3 $134.35   7.431%   $144.3335   $144.33   $144.35   $144.30  
  Purchase #4 $226.30   9.353%   $247.4658   $247.47   $247.45   $247.50  
  Purchase #5 $250.49   3.771%   $259.936   $259.94   $259.95   $259.90  
  Purchase #6 $14.77   9.583%   $16.1854   $16.19   $16.20   $16.20  
  Purchase #7 $40.47   6.750%   $43.2017   $43.20   $43.20   $43.20  
  7 purchase totals = $962.69       $1,030.5934   $1,030.60   $1,030.60   $1,030.60