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	$55.44	3.823%	$57.5595	$57.56	$57.55	$57.60
Purchase #2	$179.27	9.243%	$195.8399	$195.84	$195.85	$195.80
Purchase #3	$134.40	6.234%	$142.7785	$142.78	$142.80	$142.80
Purchase #4	$130.63	9.540%	$143.0921	$143.09	$143.10	$143.10
Purchase #5	$165.35	13.480%	$187.6392	$187.64	$187.65	$187.60
Purchase #6	$92.55	13.844%	$105.3626	$105.36	$105.35	$105.40
Purchase #7	$211.75	7.816%	$228.3004	$228.30	$228.30	$228.30
7 purchase totals =	$969.39		$1,060.5722	$1,060.57	$1,060.60	$1,060.60