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 $48.74   8.482%   $52.8741   $52.87   $52.85   $52.90  
  Purchase #2 $68.99   10.376%   $76.1484   $76.15   $76.15   $76.10  
  Purchase #3 $172.99   13.186%   $195.8005   $195.80   $195.80   $195.80  
  Purchase #4 $56.38   6.840%   $60.2364   $60.24   $60.25   $60.20  
  Purchase #5 $52.26   13.467%   $59.2979   $59.30   $59.30   $59.30  
  Purchase #6 $22.87   8.525%   $24.8197   $24.82   $24.80   $24.80  
  Purchase #7 $227.99   11.230%   $253.5933   $253.59   $253.60   $253.60  
  7 purchase totals = $650.22       $722.7703   $722.77   $722.75   $722.70