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	$91.65	9.714%	$100.5529	$100.55	$100.55	$100.60
Purchase #2	$190.34	3.180%	$196.3928	$196.39	$196.40	$196.40
Purchase #3	$127.59	10.346%	$140.7905	$140.79	$140.80	$140.80
Purchase #4	$49.26	7.207%	$52.8102	$52.81	$52.80	$52.80
Purchase #5	$98.59	11.779%	$110.2029	$110.20	$110.20	$110.20
Purchase #6	$37.95	7.224%	$40.6915	$40.69	$40.70	$40.70
Purchase #7	$77.70	11.207%	$86.4078	$86.41	$86.40	$86.40
7 purchase totals =	$673.08		$727.8486	$727.84	$727.85	$727.90