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 $84.64   8.734%   $92.0325   $92.03   $92.05   $92.00  
  Purchase #2 $5.90   7.343%   $6.3332   $6.33   $6.35   $6.30  
  Purchase #3 $86.25   12.449%   $96.9873   $96.99   $97.00   $97.00  
  Purchase #4 $180.58   13.673%   $205.2707   $205.27   $205.25   $205.30  
  Purchase #5 $23.97   3.657%   $24.8466   $24.85   $24.85   $24.80  
  Purchase #6 $100.63   13.793%   $114.5099   $114.51   $114.50   $114.50  
  Purchase #7 $167.37   7.223%   $179.4591   $179.46   $179.45   $179.50  
  7 purchase totals = $649.34       $719.4393   $719.44   $719.45   $719.40