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	$98.33	11.318%	$109.459	$109.46	$109.45	$109.50
Purchase #2	$18.91	13.816%	$21.5226	$21.52	$21.50	$21.50
Purchase #3	$226.86	9.107%	$247.5201	$247.52	$247.50	$247.50
Purchase #4	$75.28	7.655%	$81.0427	$81.04	$81.05	$81.00
Purchase #5	$21.61	10.132%	$23.7995	$23.80	$23.80	$23.80
Purchase #6	$90.92	5.873%	$96.2597	$96.26	$96.25	$96.30
Purchase #7	$64.54	4.456%	$67.4159	$67.42	$67.40	$67.40
7 purchase totals =	$596.45		$647.0195	$647.02	$646.95	$647.00