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	$199.85	9.149%	$218.1343	$218.13	$218.15	$218.10
Purchase #2	$77.70	10.694%	$86.0092	$86.01	$86.00	$86.00
Purchase #3	$182.34	13.130%	$206.2812	$206.28	$206.30	$206.30
Purchase #4	$89.96	13.265%	$101.8932	$101.89	$101.90	$101.90
Purchase #5	$122.33	12.323%	$137.4047	$137.40	$137.40	$137.40
Purchase #6	$37.76	6.653%	$40.2722	$40.27	$40.25	$40.30
Purchase #7	$149.81	4.715%	$156.8735	$156.87	$156.85	$156.90
7 purchase totals =	$859.75		$946.8683	$946.85	$946.85	$946.90