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	$143.56	11.753%	$160.4326	$160.43	$160.45	$160.40
Purchase #2	$85.87	11.131%	$95.4282	$95.43	$95.45	$95.40
Purchase #3	$211.29	4.168%	$220.0966	$220.10	$220.10	$220.10
Purchase #4	$156.30	13.176%	$176.8941	$176.89	$176.90	$176.90
Purchase #5	$242.80	3.380%	$251.0066	$251.01	$251.00	$251.00
Purchase #6	$57.27	3.333%	$59.1788	$59.18	$59.20	$59.20
Purchase #7	$237.40	11.564%	$264.8529	$264.85	$264.85	$264.90
7 purchase totals =	$1,134.49		$1,227.8898	$1,227.89	$1,227.95	$1,227.90