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 $55.79   12.868%   $62.9691   $62.97   $62.95   $63.00  
  Purchase #2 $77.42   11.113%   $86.0237   $86.02   $86.00   $86.00  
  Purchase #3 $71.34   5.745%   $75.4385   $75.44   $75.45   $75.40  
  Purchase #4 $164.28   7.324%   $176.3119   $176.31   $176.30   $176.30  
  Purchase #5 $124.51   11.233%   $138.4962   $138.50   $138.50   $138.50  
  Purchase #6 $84.31   3.139%   $86.9565   $86.96   $86.95   $87.00  
  Purchase #7 $222.94   6.638%   $237.7388   $237.74   $237.75   $237.70  
  7 purchase totals = $800.59       $863.9347   $863.94   $863.90   $863.90