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	$156.28	10.793%	$173.1473	$173.15	$173.15	$173.10
Purchase #2	$63.98	5.524%	$67.5143	$67.51	$67.50	$67.50
Purchase #3	$47.29	11.867%	$52.9019	$52.90	$52.90	$52.90
Purchase #4	$96.88	13.786%	$110.2359	$110.24	$110.25	$110.20
Purchase #5	$43.40	4.669%	$45.4263	$45.43	$45.45	$45.40
Purchase #6	$25.27	8.375%	$27.3864	$27.39	$27.40	$27.40
Purchase #7	$130.48	10.647%	$144.3722	$144.37	$144.35	$144.40
7 purchase totals =	$563.58		$620.9843	$620.99	$621.00	$620.90