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	$177.47	4.400%	$185.2787	$185.28	$185.30	$185.30
Purchase #2	$246.56	4.146%	$256.7824	$256.78	$256.80	$256.80
Purchase #3	$193.87	6.538%	$206.5452	$206.55	$206.55	$206.50
Purchase #4	$238.91	4.105%	$248.7173	$248.72	$248.70	$248.70
Purchase #5	$210.67	5.797%	$222.8825	$222.88	$222.90	$222.90
Purchase #6	$54.65	12.306%	$61.3752	$61.38	$61.40	$61.40
Purchase #7	$131.55	13.468%	$149.2672	$149.27	$149.25	$149.30
7 purchase totals =	$1,253.68		$1,330.8485	$1,330.86	$1,330.90	$1,330.90