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 $76.42   10.245%   $84.2492   $84.25   $84.25   $84.20  
  Purchase #2 $184.97   11.386%   $206.0307   $206.03   $206.05   $206.00  
  Purchase #3 $139.80   5.769%   $147.8651   $147.87   $147.85   $147.90  
  Purchase #4 $22.97   4.440%   $23.9899   $23.99   $24.00   $24.00  
  Purchase #5 $61.82   5.393%   $65.154   $65.15   $65.15   $65.20  
  Purchase #6 $45.78   11.565%   $51.0745   $51.07   $51.05   $51.10  
  Purchase #7 $118.41   12.734%   $133.4883   $133.49   $133.50   $133.50  
  7 purchase totals = $650.17       $711.8517   $711.85   $711.85   $711.90