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	$40.56	7.672%	$43.6718	$43.67	$43.65	$43.70
Purchase #2	$54.62	8.648%	$59.3435	$59.34	$59.35	$59.30
Purchase #3	$247.95	4.601%	$259.3582	$259.36	$259.35	$259.40
Purchase #4	$130.27	8.674%	$141.5696	$141.57	$141.55	$141.60
Purchase #5	$27.57	6.830%	$29.453	$29.45	$29.45	$29.50
Purchase #6	$214.85	6.696%	$229.2364	$229.24	$229.25	$229.20
Purchase #7	$210.30	12.494%	$236.5749	$236.57	$236.55	$236.60
7 purchase totals =	$926.12		$999.2074	$999.20	$999.15	$999.30