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	$200.26	12.303%	$224.898	$224.90	$224.90	$224.90
Purchase #2	$120.32	6.186%	$127.763	$127.76	$127.75	$127.80
Purchase #3	$194.27	8.408%	$210.6042	$210.60	$210.60	$210.60
Purchase #4	$192.72	13.584%	$218.8991	$218.90	$218.90	$218.90
Purchase #5	$175.58	5.355%	$184.9823	$184.98	$185.00	$185.00
Purchase #6	$46.73	4.301%	$48.7399	$48.74	$48.75	$48.70
Purchase #7	$160.42	9.443%	$175.5685	$175.57	$175.55	$175.60
7 purchase totals =	$1,090.30		$1,191.4550	$1,191.45	$1,191.45	$1,191.50