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	$150.96	11.762%	$168.7159	$168.72	$168.70	$168.70
Purchase #2	$75.55	5.766%	$79.9062	$79.91	$79.90	$79.90
Purchase #3	$92.41	11.873%	$103.3818	$103.38	$103.40	$103.40
Purchase #4	$229.43	7.703%	$247.103	$247.10	$247.10	$247.10
Purchase #5	$231.43	8.186%	$250.3749	$250.37	$250.35	$250.40
Purchase #6	$99.96	7.801%	$107.7579	$107.76	$107.75	$107.80
Purchase #7	$176.42	4.854%	$184.9834	$184.98	$185.00	$185.00
7 purchase totals =	$1,056.16		$1,142.2231	$1,142.22	$1,142.20	$1,142.30