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	$243.53	4.206%	$253.7729	$253.77	$253.75	$253.80
Purchase #2	$143.79	4.779%	$150.6617	$150.66	$150.65	$150.70
Purchase #3	$150.77	10.169%	$166.1018	$166.10	$166.10	$166.10
Purchase #4	$239.93	13.298%	$271.8359	$271.84	$271.85	$271.80
Purchase #5	$160.29	11.150%	$178.1623	$178.16	$178.15	$178.20
Purchase #6	$89.39	12.854%	$100.8802	$100.88	$100.90	$100.90
Purchase #7	$133.51	6.696%	$142.4498	$142.45	$142.45	$142.40
7 purchase totals =	$1,161.21		$1,263.8646	$1,263.86	$1,263.85	$1,263.90