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	$53.68	10.409%	$59.2676	$59.27	$59.25	$59.30
Purchase #2	$100.68	5.108%	$105.8227	$105.82	$105.80	$105.80
Purchase #3	$235.61	6.369%	$250.616	$250.62	$250.60	$250.60
Purchase #4	$142.92	6.230%	$151.8239	$151.82	$151.80	$151.80
Purchase #5	$79.90	10.566%	$88.3422	$88.34	$88.35	$88.30
Purchase #6	$60.40	13.764%	$68.7135	$68.71	$68.70	$68.70
Purchase #7	$137.29	13.784%	$156.2141	$156.21	$156.20	$156.20
7 purchase totals =	$810.48		$880.8000	$880.79	$880.70	$880.70