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	$128.79	13.438%	$146.0968	$146.10	$146.10	$146.10
Purchase #2	$205.84	7.821%	$221.9387	$221.94	$221.95	$221.90
Purchase #3	$168.84	11.698%	$188.5909	$188.59	$188.60	$188.60
Purchase #4	$146.35	11.338%	$162.9432	$162.94	$162.95	$162.90
Purchase #5	$31.40	4.385%	$32.7769	$32.78	$32.80	$32.80
Purchase #6	$112.53	12.276%	$126.3442	$126.34	$126.35	$126.30
Purchase #7	$191.39	10.312%	$211.1261	$211.13	$211.15	$211.10
7 purchase totals =	$985.14		$1,089.8168	$1,089.82	$1,089.90	$1,089.70