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	$65.42	12.799%	$73.7931	$73.79	$73.80	$73.80
Purchase #2	$199.67	11.477%	$222.5861	$222.59	$222.60	$222.60
Purchase #3	$210.62	5.632%	$222.4821	$222.48	$222.50	$222.50
Purchase #4	$159.35	4.310%	$166.218	$166.22	$166.20	$166.20
Purchase #5	$49.92	11.799%	$55.8101	$55.81	$55.80	$55.80
Purchase #6	$108.26	6.328%	$115.1107	$115.11	$115.10	$115.10
Purchase #7	$215.72	7.152%	$231.1483	$231.15	$231.15	$231.10
7 purchase totals =	$1,008.96		$1,087.1484	$1,087.15	$1,087.15	$1,087.10