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 $217.76   12.486%   $244.9495   $244.95   $244.95   $244.90  
  Purchase #2 $134.77   13.486%   $152.9451   $152.95   $152.95   $152.90  
  Purchase #3 $245.64   6.669%   $262.0217   $262.02   $262.00   $262.00  
  Purchase #4 $191.30   13.784%   $217.6688   $217.67   $217.65   $217.70  
  Purchase #5 $155.26   8.607%   $168.6232   $168.62   $168.60   $168.60  
  Purchase #6 $61.48   12.773%   $69.3328   $69.33   $69.35   $69.30  
  Purchase #7 $68.86   6.648%   $73.4378   $73.44   $73.45   $73.40  
  7 purchase totals = $1,075.07       $1,188.9789   $1,188.98   $1,188.95   $1,188.80