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	$174.51	9.736%	$191.5003	$191.50	$191.50	$191.50
Purchase #2	$46.71	8.209%	$50.5444	$50.54	$50.55	$50.50
Purchase #3	$90.39	11.402%	$100.6963	$100.70	$100.70	$100.70
Purchase #4	$87.35	10.722%	$96.7157	$96.72	$96.70	$96.70
Purchase #5	$16.58	11.596%	$18.5026	$18.50	$18.50	$18.50
Purchase #6	$118.48	9.447%	$129.6728	$129.67	$129.65	$129.70
Purchase #7	$5.45	9.314%	$5.9576	$5.96	$5.95	$6.00
7 purchase totals =	$539.47		$593.5897	$593.59	$593.55	$593.60