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	$167.81	7.335%	$180.1189	$180.12	$180.10	$180.10
Purchase #2	$15.40	4.711%	$16.1255	$16.13	$16.15	$16.10
Purchase #3	$39.89	7.568%	$42.9089	$42.91	$42.90	$42.90
Purchase #4	$41.49	4.750%	$43.4608	$43.46	$43.45	$43.50
Purchase #5	$87.98	11.727%	$98.2974	$98.30	$98.30	$98.30
Purchase #6	$90.77	5.763%	$96.0011	$96.00	$96.00	$96.00
Purchase #7	$22.27	5.167%	$23.4207	$23.42	$23.40	$23.40
7 purchase totals =	$465.61		$500.3333	$500.34	$500.30	$500.30