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	$39.91	3.171%	$41.1755	$41.18	$41.20	$41.20
Purchase #2	$77.52	6.124%	$82.2673	$82.27	$82.25	$82.30
Purchase #3	$115.49	6.684%	$123.2094	$123.21	$123.20	$123.20
Purchase #4	$131.83	4.137%	$137.2838	$137.28	$137.30	$137.30
Purchase #5	$105.43	11.411%	$117.4606	$117.46	$117.45	$117.50
Purchase #6	$200.52	5.517%	$211.5827	$211.58	$211.60	$211.60
Purchase #7	$74.32	7.188%	$79.6621	$79.66	$79.65	$79.70
7 purchase totals =	$745.02		$792.6414	$792.64	$792.65	$792.80