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	$151.63	12.292%	$170.2684	$170.27	$170.25	$170.30
Purchase #2	$176.48	13.556%	$200.4036	$200.40	$200.40	$200.40
Purchase #3	$147.81	6.476%	$157.3822	$157.38	$157.40	$157.40
Purchase #4	$40.57	3.152%	$41.8488	$41.85	$41.85	$41.80
Purchase #5	$247.44	8.816%	$269.2543	$269.25	$269.25	$269.30
Purchase #6	$189.75	13.466%	$215.3017	$215.30	$215.30	$215.30
Purchase #7	$59.48	13.232%	$67.3504	$67.35	$67.35	$67.40
7 purchase totals =	$1,013.16		$1,121.8094	$1,121.80	$1,121.80	$1,121.90