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	$29.53	7.137%	$31.6376	$31.64	$31.65	$31.60
Purchase #2	$148.73	10.720%	$164.6739	$164.67	$164.65	$164.70
Purchase #3	$178.48	12.493%	$200.7775	$200.78	$200.80	$200.80
Purchase #4	$136.94	4.499%	$143.1009	$143.10	$143.10	$143.10
Purchase #5	$145.62	9.607%	$159.6097	$159.61	$159.60	$159.60
Purchase #6	$170.45	8.614%	$185.1326	$185.13	$185.15	$185.10
Purchase #7	$64.50	10.813%	$71.4744	$71.47	$71.45	$71.50
7 purchase totals =	$874.25		$956.4066	$956.40	$956.40	$956.40