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	$20.64	12.492%	$23.2183	$23.22	$23.20	$23.20
Purchase #2	$237.41	11.331%	$264.3109	$264.31	$264.30	$264.30
Purchase #3	$244.99	10.666%	$271.1206	$271.12	$271.10	$271.10
Purchase #4	$45.29	12.370%	$50.8924	$50.89	$50.90	$50.90
Purchase #5	$165.72	9.688%	$181.775	$181.78	$181.80	$181.80
Purchase #6	$91.85	12.776%	$103.5848	$103.58	$103.60	$103.60
Purchase #7	$131.73	9.808%	$144.6501	$144.65	$144.65	$144.70
7 purchase totals =	$937.63		$1,039.5521	$1,039.55	$1,039.55	$1,039.60