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	$185.44	6.129%	$196.8056	$196.81	$196.80	$196.80
Purchase #2	$134.67	3.669%	$139.611	$139.61	$139.60	$139.60
Purchase #3	$199.80	5.132%	$210.0537	$210.05	$210.05	$210.10
Purchase #4	$210.83	10.758%	$233.5111	$233.51	$233.50	$233.50
Purchase #5	$82.32	12.107%	$92.2865	$92.29	$92.30	$92.30
Purchase #6	$209.60	8.380%	$227.1645	$227.16	$227.15	$227.20
Purchase #7	$25.93	8.161%	$28.0461	$28.05	$28.05	$28.00
7 purchase totals =	$1,048.59		$1,127.4785	$1,127.48	$1,127.45	$1,127.50