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 $72.26   5.523%   $76.2509   $76.25   $76.25   $76.30  
  Purchase #2 $236.73   7.188%   $253.7462   $253.75   $253.75   $253.70  
  Purchase #3 $126.98   8.838%   $138.2025   $138.20   $138.20   $138.20  
  Purchase #4 $194.43   6.498%   $207.0641   $207.06   $207.05   $207.10  
  Purchase #5 $8.74   7.359%   $9.3832   $9.38   $9.40   $9.40  
  Purchase #6 $70.81   6.860%   $75.6676   $75.67   $75.65   $75.70  
  Purchase #7 $198.95   13.659%   $226.1246   $226.12   $226.10   $226.10  
  7 purchase totals = $908.90       $986.4391   $986.43   $986.40   $986.50