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	$120.65	8.278%	$130.6374	$130.64	$130.65	$130.60
Purchase #2	$88.30	12.418%	$99.2651	$99.27	$99.25	$99.30
Purchase #3	$226.50	12.741%	$255.3584	$255.36	$255.35	$255.40
Purchase #4	$141.79	4.208%	$147.7565	$147.76	$147.75	$147.80
Purchase #5	$241.97	4.618%	$253.1442	$253.14	$253.15	$253.10
Purchase #6	$174.59	13.711%	$198.528	$198.53	$198.55	$198.50
Purchase #7	$233.72	10.340%	$257.8866	$257.89	$257.90	$257.90
7 purchase totals =	$1,227.52		$1,342.5762	$1,342.59	$1,342.60	$1,342.60