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	$85.76	4.373%	$89.5103	$89.51	$89.50	$89.50
Purchase #2	$92.65	4.292%	$96.6265	$96.63	$96.65	$96.60
Purchase #3	$204.45	6.564%	$217.8701	$217.87	$217.85	$217.90
Purchase #4	$135.82	5.840%	$143.7519	$143.75	$143.75	$143.80
Purchase #5	$158.37	12.317%	$177.8764	$177.88	$177.90	$177.90
Purchase #6	$54.42	7.431%	$58.464	$58.46	$58.45	$58.50
Purchase #7	$37.58	10.746%	$41.6183	$41.62	$41.60	$41.60
7 purchase totals =	$769.05		$825.7175	$825.72	$825.70	$825.80