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	$72.50	6.384%	$77.1284	$77.13	$77.15	$77.10
Purchase #2	$176.42	5.280%	$185.735	$185.74	$185.75	$185.70
Purchase #3	$172.41	10.117%	$189.8527	$189.85	$189.85	$189.90
Purchase #4	$116.87	6.184%	$124.0972	$124.10	$124.10	$124.10
Purchase #5	$232.25	7.786%	$250.333	$250.33	$250.35	$250.30
Purchase #6	$161.78	11.192%	$179.8864	$179.89	$179.90	$179.90
Purchase #7	$134.73	3.335%	$139.2232	$139.22	$139.20	$139.20
7 purchase totals =	$1,066.96		$1,146.2559	$1,146.26	$1,146.30	$1,146.20