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 $62.98   5.166%   $66.2335   $66.23   $66.25   $66.20  
  Purchase #2 $118.99   10.649%   $131.6612   $131.66   $131.65   $131.70  
  Purchase #3 $25.38   4.759%   $26.5878   $26.59   $26.60   $26.60  
  Purchase #4 $96.30   6.481%   $102.5412   $102.54   $102.55   $102.50  
  Purchase #5 $63.91   11.566%   $71.3018   $71.30   $71.30   $71.30  
  Purchase #6 $63.41   3.762%   $65.7955   $65.80   $65.80   $65.80  
  Purchase #7 $31.72   12.338%   $35.6336   $35.63   $35.65   $35.60  
  7 purchase totals = $462.69       $499.7546   $499.75   $499.80   $499.70