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	$232.38	11.189%	$258.381	$258.38	$258.40	$258.40
Purchase #2	$49.26	12.697%	$55.5145	$55.51	$55.50	$55.50
Purchase #3	$142.64	8.115%	$154.2152	$154.22	$154.20	$154.20
Purchase #4	$118.47	11.230%	$131.7742	$131.77	$131.75	$131.80
Purchase #5	$102.58	6.793%	$109.5483	$109.55	$109.55	$109.50
Purchase #6	$209.33	12.322%	$235.1236	$235.12	$235.10	$235.10
Purchase #7	$127.53	12.164%	$143.0427	$143.04	$143.05	$143.00
7 purchase totals =	$982.19		$1,087.5995	$1,087.59	$1,087.55	$1,087.50