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 $65.38   3.278%   $67.5232   $67.52   $67.50   $67.50  
  Purchase #2 $105.39   13.853%   $119.9897   $119.99   $120.00   $120.00  
  Purchase #3 $149.41   10.179%   $164.6184   $164.62   $164.60   $164.60  
  Purchase #4 $97.87   8.318%   $106.0108   $106.01   $106.00   $106.00  
  Purchase #5 $245.94   4.818%   $257.7894   $257.79   $257.80   $257.80  
  Purchase #6 $164.56   7.106%   $176.2536   $176.25   $176.25   $176.30  
  Purchase #7 $70.35   6.704%   $75.0663   $75.07   $75.05   $75.10  
  7 purchase totals = $898.90       $967.2514   $967.25   $967.20   $967.30