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	$154.98	11.329%	$172.5377	$172.54	$172.55	$172.50
Purchase #2	$185.26	10.279%	$204.3029	$204.30	$204.30	$204.30
Purchase #3	$21.32	10.541%	$23.5673	$23.57	$23.55	$23.60
Purchase #4	$75.87	5.667%	$80.1696	$80.17	$80.15	$80.20
Purchase #5	$86.59	3.627%	$89.7306	$89.73	$89.75	$89.70
Purchase #6	$227.99	9.529%	$249.7152	$249.72	$249.70	$249.70
Purchase #7	$121.45	8.113%	$131.3032	$131.30	$131.30	$131.30
7 purchase totals =	$873.46		$951.3265	$951.33	$951.30	$951.30