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 $93.64   13.251%   $106.0482   $106.05   $106.05   $106.00  
  Purchase #2 $229.95   9.777%   $252.4322   $252.43   $252.45   $252.40  
  Purchase #3 $162.91   10.472%   $179.9699   $179.97   $179.95   $180.00  
  Purchase #4 $241.76   8.424%   $262.1259   $262.13   $262.15   $262.10  
  Purchase #5 $6.93   4.786%   $7.2617   $7.26   $7.25   $7.30  
  Purchase #6 $42.72   8.169%   $46.2098   $46.21   $46.20   $46.20  
  Purchase #7 $107.66   10.262%   $118.7081   $118.71   $118.70   $118.70  
  7 purchase totals = $885.57       $972.7558   $972.76   $972.75   $972.70