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	$16.57	13.863%	$18.8671	$18.87	$18.85	$18.90
Purchase #2	$160.57	3.485%	$166.1659	$166.17	$166.15	$166.20
Purchase #3	$196.73	13.574%	$223.4341	$223.43	$223.45	$223.40
Purchase #4	$41.41	10.586%	$45.7937	$45.79	$45.80	$45.80
Purchase #5	$85.92	5.341%	$90.509	$90.51	$90.50	$90.50
Purchase #6	$250.45	5.799%	$264.9736	$264.97	$264.95	$265.00
Purchase #7	$109.84	3.841%	$114.059	$114.06	$114.05	$114.10
7 purchase totals =	$861.49		$923.8024	$923.80	$923.75	$923.90