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	$96.73	3.181%	$99.807	$99.81	$99.80	$99.80
Purchase #2	$131.36	8.735%	$142.8343	$142.83	$142.85	$142.80
Purchase #3	$66.58	5.635%	$70.3318	$70.33	$70.35	$70.30
Purchase #4	$18.90	7.831%	$20.3801	$20.38	$20.40	$20.40
Purchase #5	$92.39	11.231%	$102.7663	$102.77	$102.75	$102.80
Purchase #6	$35.34	12.271%	$39.6766	$39.68	$39.70	$39.70
Purchase #7	$149.79	10.716%	$165.8415	$165.84	$165.85	$165.80
7 purchase totals =	$591.09		$641.6376	$641.64	$641.70	$641.60