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	$177.38	6.644%	$189.1651	$189.17	$189.15	$189.20
Purchase #2	$97.62	7.843%	$105.2763	$105.28	$105.30	$105.30
Purchase #3	$145.96	10.531%	$161.331	$161.33	$161.35	$161.30
Purchase #4	$86.54	4.134%	$90.1176	$90.12	$90.10	$90.10
Purchase #5	$216.54	13.500%	$245.7729	$245.77	$245.75	$245.80
Purchase #6	$46.90	3.699%	$48.6348	$48.63	$48.65	$48.60
Purchase #7	$216.39	4.494%	$226.1146	$226.11	$226.10	$226.10
7 purchase totals =	$987.33		$1,066.4123	$1,066.41	$1,066.40	$1,066.40