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 $26.64   4.261%   $27.7751   $27.78   $27.80   $27.80  
  Purchase #2 $220.62   11.182%   $245.2897   $245.29   $245.30   $245.30  
  Purchase #3 $242.36   8.859%   $263.8307   $263.83   $263.85   $263.80  
  Purchase #4 $8.96   6.648%   $9.5557   $9.56   $9.55   $9.60  
  Purchase #5 $139.61   8.177%   $151.0259   $151.03   $151.05   $151.00  
  Purchase #6 $206.91   3.542%   $214.2388   $214.24   $214.25   $214.20  
  Purchase #7 $107.82   6.752%   $115.1   $115.10   $115.10   $115.10  
  7 purchase totals = $952.92       $1,026.8159   $1,026.83   $1,026.90   $1,026.80