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	$143.55	11.291%	$159.7582	$159.76	$159.75	$159.80
Purchase #2	$29.87	5.585%	$31.5382	$31.54	$31.55	$31.50
Purchase #3	$19.90	3.118%	$20.5205	$20.52	$20.50	$20.50
Purchase #4	$10.87	7.221%	$11.6549	$11.65	$11.65	$11.70
Purchase #5	$18.88	12.640%	$21.2664	$21.27	$21.25	$21.30
Purchase #6	$236.53	4.629%	$247.479	$247.48	$247.50	$247.50
Purchase #7	$172.49	3.609%	$178.7152	$178.72	$178.70	$178.70
7 purchase totals =	$632.09		$670.9324	$670.94	$670.90	$671.00