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	$151.64	13.680%	$172.3844	$172.38	$172.40	$172.40
Purchase #2	$42.33	3.252%	$43.7066	$43.71	$43.70	$43.70
Purchase #3	$173.37	7.351%	$186.1144	$186.11	$186.10	$186.10
Purchase #4	$130.73	6.257%	$138.9098	$138.91	$138.90	$138.90
Purchase #5	$72.62	7.853%	$78.3228	$78.32	$78.30	$78.30
Purchase #6	$25.57	10.480%	$28.2497	$28.25	$28.25	$28.20
Purchase #7	$123.92	13.690%	$140.8846	$140.88	$140.90	$140.90
7 purchase totals =	$720.18		$788.5723	$788.56	$788.55	$788.50