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 $43.74   5.767%   $46.2625   $46.26   $46.25   $46.30  
  Purchase #2 $98.69   8.164%   $106.7471   $106.75   $106.75   $106.70  
  Purchase #3 $57.93   10.159%   $63.8151   $63.82   $63.80   $63.80  
  Purchase #4 $135.59   13.820%   $154.3285   $154.33   $154.35   $154.30  
  Purchase #5 $76.54   10.283%   $84.4106   $84.41   $84.40   $84.40  
  Purchase #6 $211.50   7.290%   $226.9184   $226.92   $226.90   $226.90  
  Purchase #7 $105.82   4.823%   $110.9237   $110.92   $110.90   $110.90  
  7 purchase totals = $729.81       $793.4059   $793.41   $793.35   $793.30