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	$200.55	6.607%	$213.8003	$213.80	$213.80	$213.80
Purchase #2	$72.65	9.229%	$79.3549	$79.35	$79.35	$79.40
Purchase #3	$72.28	9.117%	$78.8698	$78.87	$78.85	$78.90
Purchase #4	$230.57	7.485%	$247.8282	$247.83	$247.85	$247.80
Purchase #5	$242.30	12.760%	$273.2175	$273.22	$273.20	$273.20
Purchase #6	$102.35	6.765%	$109.274	$109.27	$109.25	$109.30
Purchase #7	$244.45	12.665%	$275.4096	$275.41	$275.40	$275.40
7 purchase totals =	$1,165.15		$1,277.7543	$1,277.75	$1,277.70	$1,277.80