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	$28.60	8.573%	$31.0519	$31.05	$31.05	$31.10
Purchase #2	$217.28	12.503%	$244.4465	$244.45	$244.45	$244.40
Purchase #3	$17.68	9.277%	$19.3202	$19.32	$19.30	$19.30
Purchase #4	$196.82	12.594%	$221.6075	$221.61	$221.60	$221.60
Purchase #5	$38.87	6.680%	$41.4665	$41.47	$41.45	$41.50
Purchase #6	$107.30	6.133%	$113.8807	$113.88	$113.90	$113.90
Purchase #7	$179.49	11.717%	$200.5208	$200.52	$200.50	$200.50
7 purchase totals =	$786.04		$872.2941	$872.30	$872.25	$872.30