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	$212.67	5.871%	$225.1559	$225.16	$225.15	$225.20
Purchase #2	$207.55	8.180%	$224.5276	$224.53	$224.55	$224.50
Purchase #3	$58.31	12.762%	$65.7515	$65.75	$65.75	$65.80
Purchase #4	$52.89	4.747%	$55.4007	$55.40	$55.40	$55.40
Purchase #5	$172.35	8.718%	$187.3755	$187.38	$187.40	$187.40
Purchase #6	$82.96	9.183%	$90.5782	$90.58	$90.60	$90.60
Purchase #7	$47.90	11.642%	$53.4765	$53.48	$53.50	$53.50
7 purchase totals =	$834.63		$902.2659	$902.28	$902.35	$902.40