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	$38.57	9.496%	$42.2326	$42.23	$42.25	$42.20
Purchase #2	$11.53	3.421%	$11.9244	$11.92	$11.90	$11.90
Purchase #3	$16.91	7.849%	$18.2373	$18.24	$18.25	$18.20
Purchase #4	$181.70	6.465%	$193.4469	$193.45	$193.45	$193.40
Purchase #5	$59.42	13.637%	$67.5231	$67.52	$67.50	$67.50
Purchase #6	$120.66	11.818%	$134.9196	$134.92	$134.90	$134.90
Purchase #7	$151.96	4.232%	$158.3909	$158.39	$158.40	$158.40
7 purchase totals =	$580.75		$626.6748	$626.67	$626.65	$626.50