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	$27.42	3.533%	$28.3887	$28.39	$28.40	$28.40
Purchase #2	$71.69	6.873%	$76.6173	$76.62	$76.60	$76.60
Purchase #3	$162.97	3.518%	$168.7033	$168.70	$168.70	$168.70
Purchase #4	$13.98	12.522%	$15.7306	$15.73	$15.75	$15.70
Purchase #5	$112.64	13.356%	$127.6842	$127.68	$127.70	$127.70
Purchase #6	$116.39	11.696%	$130.003	$130.00	$130.00	$130.00
Purchase #7	$85.45	4.468%	$89.2679	$89.27	$89.25	$89.30
7 purchase totals =	$590.54		$636.3950	$636.39	$636.40	$636.40