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	$157.72	5.723%	$166.7463	$166.75	$166.75	$166.70
Purchase #2	$63.30	6.373%	$67.3341	$67.33	$67.35	$67.30
Purchase #3	$222.69	13.323%	$252.359	$252.36	$252.35	$252.40
Purchase #4	$201.90	9.594%	$221.2703	$221.27	$221.25	$221.30
Purchase #5	$113.49	13.547%	$128.8645	$128.86	$128.85	$128.90
Purchase #6	$109.30	8.375%	$118.4539	$118.45	$118.45	$118.50
Purchase #7	$25.42	13.644%	$28.8883	$28.89	$28.90	$28.90
7 purchase totals =	$893.82		$983.9164	$983.91	$983.90	$984.00