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	$116.51	3.470%	$120.5529	$120.55	$120.55	$120.60
Purchase #2	$158.39	4.673%	$165.7916	$165.79	$165.80	$165.80
Purchase #3	$218.43	13.736%	$248.4335	$248.43	$248.45	$248.40
Purchase #4	$101.30	4.180%	$105.5343	$105.53	$105.55	$105.50
Purchase #5	$197.30	11.663%	$220.3111	$220.31	$220.30	$220.30
Purchase #6	$169.69	13.757%	$193.0343	$193.03	$193.05	$193.00
Purchase #7	$38.53	4.194%	$40.1459	$40.15	$40.15	$40.10
7 purchase totals =	$1,000.15		$1,093.8036	$1,093.79	$1,093.85	$1,093.70