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	$16.89	9.192%	$18.4425	$18.44	$18.45	$18.40
Purchase #2	$95.64	4.385%	$99.8338	$99.83	$99.85	$99.80
Purchase #3	$44.72	7.764%	$48.1921	$48.19	$48.20	$48.20
Purchase #4	$18.62	3.862%	$19.3391	$19.34	$19.35	$19.30
Purchase #5	$65.27	11.162%	$72.5554	$72.56	$72.55	$72.60
Purchase #6	$186.94	3.727%	$193.9073	$193.91	$193.90	$193.90
Purchase #7	$239.46	3.849%	$248.6768	$248.68	$248.70	$248.70
7 purchase totals =	$667.54		$700.9470	$700.95	$701.00	$700.90