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 $239.93   10.716%   $265.6409   $265.64   $265.65   $265.60  
  Purchase #2 $208.70   12.228%   $234.2198   $234.22   $234.20   $234.20  
  Purchase #3 $233.86   9.492%   $256.058   $256.06   $256.05   $256.10  
  Purchase #4 $90.40   3.648%   $93.6978   $93.70   $93.70   $93.70  
  Purchase #5 $201.29   11.106%   $223.6453   $223.65   $223.65   $223.60  
  Purchase #6 $244.90   13.522%   $278.0154   $278.02   $278.00   $278.00  
  Purchase #7 $209.47   3.766%   $217.3586   $217.36   $217.35   $217.40  
  7 purchase totals = $1,428.55       $1,568.6358   $1,568.65   $1,568.60   $1,568.60