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	$250.72	6.320%	$266.5655	$266.57	$266.55	$266.60
Purchase #2	$53.29	12.381%	$59.8878	$59.89	$59.90	$59.90
Purchase #3	$119.79	9.144%	$130.7436	$130.74	$130.75	$130.70
Purchase #4	$34.75	7.217%	$37.2579	$37.26	$37.25	$37.30
Purchase #5	$116.88	8.344%	$126.6325	$126.63	$126.65	$126.60
Purchase #6	$42.57	3.186%	$43.9263	$43.93	$43.95	$43.90
Purchase #7	$22.72	5.192%	$23.8996	$23.90	$23.90	$23.90
7 purchase totals =	$640.72		$688.9132	$688.92	$688.95	$688.90