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	$59.39	13.105%	$67.1731	$67.17	$67.15	$67.20
Purchase #2	$131.30	7.187%	$140.7365	$140.74	$140.75	$140.70
Purchase #3	$244.46	12.512%	$275.0468	$275.05	$275.05	$275.00
Purchase #4	$230.53	8.586%	$250.3233	$250.32	$250.30	$250.30
Purchase #5	$159.91	7.746%	$172.2966	$172.30	$172.30	$172.30
Purchase #6	$116.56	13.600%	$132.4122	$132.41	$132.40	$132.40
Purchase #7	$150.91	9.804%	$165.7052	$165.71	$165.70	$165.70
7 purchase totals =	$1,093.06		$1,203.6937	$1,203.70	$1,203.65	$1,203.60