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	$186.71	12.767%	$210.5473	$210.55	$210.55	$210.50
Purchase #2	$107.59	8.749%	$117.003	$117.00	$117.00	$117.00
Purchase #3	$187.57	4.268%	$195.5755	$195.58	$195.60	$195.60
Purchase #4	$137.91	9.281%	$150.7094	$150.71	$150.70	$150.70
Purchase #5	$117.85	10.825%	$130.6073	$130.61	$130.60	$130.60
Purchase #6	$40.52	4.384%	$42.2964	$42.30	$42.30	$42.30
Purchase #7	$50.44	13.766%	$57.3836	$57.38	$57.40	$57.40
7 purchase totals =	$828.59		$904.1225	$904.13	$904.15	$904.10