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	$44.49	13.390%	$50.4472	$50.45	$50.45	$50.40
Purchase #2	$151.56	3.512%	$156.8828	$156.88	$156.90	$156.90
Purchase #3	$234.67	6.377%	$249.6349	$249.63	$249.65	$249.60
Purchase #4	$211.28	8.710%	$229.6825	$229.68	$229.70	$229.70
Purchase #5	$211.88	12.685%	$238.757	$238.76	$238.75	$238.80
Purchase #6	$38.85	7.808%	$41.8834	$41.88	$41.90	$41.90
Purchase #7	$68.92	13.244%	$78.0478	$78.05	$78.05	$78.00
7 purchase totals =	$961.65		$1,045.3356	$1,045.33	$1,045.40	$1,045.30