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	$44.57	5.553%	$47.045	$47.05	$47.05	$47.00
Purchase #2	$96.38	4.224%	$100.4511	$100.45	$100.45	$100.50
Purchase #3	$17.44	4.349%	$18.1985	$18.20	$18.20	$18.20
Purchase #4	$46.94	7.562%	$50.4896	$50.49	$50.50	$50.50
Purchase #5	$50.44	9.820%	$55.3932	$55.39	$55.40	$55.40
Purchase #6	$140.72	11.420%	$156.7902	$156.79	$156.80	$156.80
Purchase #7	$234.45	6.703%	$250.1652	$250.17	$250.15	$250.20
7 purchase totals =	$630.94		$678.5328	$678.54	$678.55	$678.60