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 $14.60   6.221%   $15.5083   $15.51   $15.50   $15.50  
  Purchase #2 $144.85   6.278%   $153.9437   $153.94   $153.95   $153.90  
  Purchase #3 $46.34   4.116%   $48.2474   $48.25   $48.25   $48.20  
  Purchase #4 $214.42   9.631%   $235.0708   $235.07   $235.05   $235.10  
  Purchase #5 $167.62   5.238%   $176.3999   $176.40   $176.40   $176.40  
  Purchase #6 $100.38   9.273%   $109.6882   $109.69   $109.70   $109.70  
  Purchase #7 $195.52   7.831%   $210.8312   $210.83   $210.85   $210.80  
  7 purchase totals = $883.73       $949.6895   $949.69   $949.70   $949.60