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	$219.88	6.589%	$234.3679	$234.37	$234.35	$234.40
Purchase #2	$111.98	13.869%	$127.5105	$127.51	$127.50	$127.50
Purchase #3	$196.33	5.193%	$206.5254	$206.53	$206.55	$206.50
Purchase #4	$204.61	11.334%	$227.8005	$227.80	$227.80	$227.80
Purchase #5	$201.67	3.708%	$209.1479	$209.15	$209.15	$209.10
Purchase #6	$79.68	7.826%	$85.9158	$85.92	$85.90	$85.90
Purchase #7	$44.62	12.433%	$50.1676	$50.17	$50.15	$50.20
7 purchase totals =	$1,058.77		$1,141.4356	$1,141.45	$1,141.40	$1,141.40