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	$160.93	4.855%	$168.7432	$168.74	$168.75	$168.70
Purchase #2	$165.51	8.234%	$179.1381	$179.14	$179.15	$179.10
Purchase #3	$39.99	5.668%	$42.2566	$42.26	$42.25	$42.30
Purchase #4	$126.90	7.253%	$136.1041	$136.10	$136.10	$136.10
Purchase #5	$175.62	11.662%	$196.1008	$196.10	$196.10	$196.10
Purchase #6	$122.87	5.173%	$129.2261	$129.23	$129.25	$129.20
Purchase #7	$37.45	13.555%	$42.5263	$42.53	$42.55	$42.50
7 purchase totals =	$829.27		$894.0952	$894.10	$894.15	$894.00