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	$162.53	10.359%	$179.3665	$179.37	$179.35	$179.40
Purchase #2	$157.75	13.817%	$179.5463	$179.55	$179.55	$179.50
Purchase #3	$195.80	5.231%	$206.0423	$206.04	$206.05	$206.00
Purchase #4	$58.30	12.824%	$65.7764	$65.78	$65.80	$65.80
Purchase #5	$85.30	5.760%	$90.2133	$90.21	$90.20	$90.20
Purchase #6	$38.33	9.132%	$41.8303	$41.83	$41.85	$41.80
Purchase #7	$203.88	12.261%	$228.8777	$228.88	$228.90	$228.90
7 purchase totals =	$901.89		$991.6528	$991.66	$991.70	$991.60