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 $98.73   13.171%   $111.7337   $111.73   $111.75   $111.70  
  Purchase #2 $176.52   11.626%   $197.0422   $197.04   $197.05   $197.00  
  Purchase #3 $5.45   5.619%   $5.7562   $5.76   $5.75   $5.80  
  Purchase #4 $95.45   10.344%   $105.3233   $105.32   $105.30   $105.30  
  Purchase #5 $221.55   5.845%   $234.4996   $234.50   $234.50   $234.50  
  Purchase #6 $157.36   10.600%   $174.0402   $174.04   $174.05   $174.00  
  Purchase #7 $171.38   13.712%   $194.8796   $194.88   $194.90   $194.90  
  7 purchase totals = $926.44       $1,023.2748   $1,023.27   $1,023.30   $1,023.20