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	$199.49	10.346%	$220.1292	$220.13	$220.15	$220.10
Purchase #2	$65.25	8.116%	$70.5457	$70.55	$70.55	$70.50
Purchase #3	$100.30	9.569%	$109.8977	$109.90	$109.90	$109.90
Purchase #4	$57.73	10.675%	$63.8927	$63.89	$63.90	$63.90
Purchase #5	$87.61	4.344%	$91.4158	$91.42	$91.40	$91.40
Purchase #6	$66.36	7.213%	$71.1465	$71.15	$71.15	$71.10
Purchase #7	$126.48	10.449%	$139.6959	$139.70	$139.70	$139.70
7 purchase totals =	$703.22		$766.7235	$766.74	$766.75	$766.60