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	$73.31	12.527%	$82.4935	$82.49	$82.50	$82.50
Purchase #2	$102.42	13.306%	$116.048	$116.05	$116.05	$116.00
Purchase #3	$62.34	8.557%	$67.6744	$67.67	$67.65	$67.70
Purchase #4	$77.90	8.596%	$84.5963	$84.60	$84.60	$84.60
Purchase #5	$50.77	7.259%	$54.4554	$54.46	$54.45	$54.50
Purchase #6	$70.46	8.663%	$76.5639	$76.56	$76.55	$76.60
Purchase #7	$107.51	4.468%	$112.3135	$112.31	$112.30	$112.30
7 purchase totals =	$544.71		$594.1450	$594.14	$594.10	$594.20