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 $244.76   6.636%   $261.0023   $261.00   $261.00   $261.00  
  Purchase #2 $88.34   9.511%   $96.742   $96.74   $96.75   $96.70  
  Purchase #3 $33.99   10.556%   $37.578   $37.58   $37.60   $37.60  
  Purchase #4 $84.43   11.398%   $94.0533   $94.05   $94.05   $94.10  
  Purchase #5 $103.70   11.158%   $115.2708   $115.27   $115.25   $115.30  
  Purchase #6 $28.38   3.375%   $29.3378   $29.34   $29.35   $29.30  
  Purchase #7 $181.96   6.264%   $193.358   $193.36   $193.35   $193.40  
  7 purchase totals = $765.56       $827.3422   $827.34   $827.35   $827.40