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	$79.56	12.493%	$89.4994	$89.50	$89.50	$89.50
Purchase #2	$245.59	9.646%	$269.2796	$269.28	$269.30	$269.30
Purchase #3	$231.45	5.243%	$243.5849	$243.58	$243.60	$243.60
Purchase #4	$197.72	7.601%	$212.7487	$212.75	$212.75	$212.70
Purchase #5	$47.41	10.521%	$52.398	$52.40	$52.40	$52.40
Purchase #6	$139.45	5.294%	$146.8325	$146.83	$146.85	$146.80
Purchase #7	$59.90	9.427%	$65.5468	$65.55	$65.55	$65.50
7 purchase totals =	$1,001.08		$1,079.8899	$1,079.89	$1,079.95	$1,079.80