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 $236.55   12.193%   $265.3925   $265.39   $265.40   $265.40  
  Purchase #2 $153.92   13.165%   $174.1836   $174.18   $174.20   $174.20  
  Purchase #3 $107.32   11.744%   $119.9237   $119.92   $119.90   $119.90  
  Purchase #4 $57.54   5.192%   $60.5275   $60.53   $60.55   $60.50  
  Purchase #5 $163.71   13.205%   $185.3279   $185.33   $185.35   $185.30  
  Purchase #6 $150.79   7.472%   $162.057   $162.06   $162.05   $162.10  
  Purchase #7 $99.25   8.828%   $108.0118   $108.01   $108.00   $108.00  
  7 purchase totals = $969.08       $1,075.4240   $1,075.42   $1,075.45   $1,075.40