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 $28.94   5.111%   $30.4191   $30.42   $30.40   $30.40  
  Purchase #2 $164.73   5.821%   $174.3189   $174.32   $174.30   $174.30  
  Purchase #3 $19.44   8.303%   $21.0541   $21.05   $21.05   $21.10  
  Purchase #4 $20.38   12.187%   $22.8637   $22.86   $22.85   $22.90  
  Purchase #5 $150.80   9.838%   $165.6357   $165.64   $165.65   $165.60  
  Purchase #6 $142.77   13.874%   $162.5779   $162.58   $162.60   $162.60  
  Purchase #7 $21.42   13.232%   $24.2543   $24.25   $24.25   $24.30  
  7 purchase totals = $548.48       $601.1237   $601.12   $601.10   $601.20