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 $244.25   13.214%   $276.5252   $276.53   $276.55   $276.50  
  Purchase #2 $96.94   3.114%   $99.9587   $99.96   $99.95   $100.00  
  Purchase #3 $228.69   12.125%   $256.4187   $256.42   $256.40   $256.40  
  Purchase #4 $121.63   3.798%   $126.2495   $126.25   $126.25   $126.20  
  Purchase #5 $233.59   10.494%   $258.1029   $258.10   $258.10   $258.10  
  Purchase #6 $157.90   4.676%   $165.2834   $165.28   $165.30   $165.30  
  Purchase #7 $152.30   9.396%   $166.6101   $166.61   $166.60   $166.60  
  7 purchase totals = $1,235.30       $1,349.1485   $1,349.15   $1,349.15   $1,349.10