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	$163.91	12.303%	$184.0758	$184.08	$184.10	$184.10
Purchase #2	$201.34	10.487%	$222.4545	$222.45	$222.45	$222.50
Purchase #3	$121.40	12.281%	$136.3091	$136.31	$136.30	$136.30
Purchase #4	$79.42	13.684%	$90.2878	$90.29	$90.30	$90.30
Purchase #5	$123.54	4.229%	$128.7645	$128.76	$128.75	$128.80
Purchase #6	$94.94	5.657%	$100.3108	$100.31	$100.30	$100.30
Purchase #7	$216.43	11.607%	$241.551	$241.55	$241.55	$241.60
7 purchase totals =	$1,000.98		$1,103.7535	$1,103.75	$1,103.75	$1,103.90