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	$159.25	13.613%	$180.9287	$180.93	$180.95	$180.90
Purchase #2	$60.43	11.588%	$67.4326	$67.43	$67.45	$67.40
Purchase #3	$83.99	13.499%	$95.3278	$95.33	$95.35	$95.30
Purchase #4	$61.96	3.741%	$64.2779	$64.28	$64.30	$64.30
Purchase #5	$65.41	8.621%	$71.049	$71.05	$71.05	$71.00
Purchase #6	$72.61	11.255%	$80.7823	$80.78	$80.80	$80.80
Purchase #7	$236.31	8.220%	$255.7347	$255.73	$255.75	$255.70
7 purchase totals =	$739.96		$815.5330	$815.53	$815.65	$815.40