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	$137.46	6.538%	$146.4471	$146.45	$146.45	$146.40
Purchase #2	$241.71	11.462%	$269.4148	$269.41	$269.40	$269.40
Purchase #3	$37.67	7.525%	$40.5047	$40.50	$40.50	$40.50
Purchase #4	$53.30	6.663%	$56.8514	$56.85	$56.85	$56.90
Purchase #5	$57.63	12.393%	$64.7721	$64.77	$64.75	$64.80
Purchase #6	$154.95	7.501%	$166.5728	$166.57	$166.55	$166.60
Purchase #7	$172.53	13.218%	$195.335	$195.34	$195.35	$195.30
7 purchase totals =	$855.25		$939.8979	$939.89	$939.85	$939.90