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 $118.84   4.561%   $124.2603   $124.26   $124.25   $124.30  
  Purchase #2 $71.90   9.848%   $78.9807   $78.98   $79.00   $79.00  
  Purchase #3 $136.69   12.825%   $154.2205   $154.22   $154.20   $154.20  
  Purchase #4 $211.76   4.515%   $221.321   $221.32   $221.30   $221.30  
  Purchase #5 $232.53   11.411%   $259.064   $259.06   $259.05   $259.10  
  Purchase #6 $234.79   5.132%   $246.8394   $246.84   $246.85   $246.80  
  Purchase #7 $199.30   5.394%   $210.0502   $210.05   $210.05   $210.10  
  7 purchase totals = $1,205.81       $1,294.7361   $1,294.73   $1,294.70   $1,294.80