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	$223.96	6.391%	$238.2733	$238.27	$238.25	$238.30
Purchase #2	$111.54	8.229%	$120.7186	$120.72	$120.70	$120.70
Purchase #3	$193.72	9.349%	$211.8309	$211.83	$211.85	$211.80
Purchase #4	$234.83	10.570%	$259.6515	$259.65	$259.65	$259.70
Purchase #5	$167.82	7.110%	$179.752	$179.75	$179.75	$179.80
Purchase #6	$216.88	8.152%	$234.5601	$234.56	$234.55	$234.60
Purchase #7	$96.83	3.862%	$100.5696	$100.57	$100.55	$100.60
7 purchase totals =	$1,245.58		$1,345.3560	$1,345.35	$1,345.30	$1,345.50