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	$158.56	13.163%	$179.4313	$179.43	$179.45	$179.40
Purchase #2	$33.90	3.545%	$35.1018	$35.10	$35.10	$35.10
Purchase #3	$234.80	12.292%	$263.6616	$263.66	$263.65	$263.70
Purchase #4	$107.38	4.440%	$112.1477	$112.15	$112.15	$112.10
Purchase #5	$86.57	4.257%	$90.2553	$90.26	$90.25	$90.30
Purchase #6	$35.50	13.423%	$40.2652	$40.27	$40.25	$40.30
Purchase #7	$165.80	10.500%	$183.209	$183.21	$183.20	$183.20
7 purchase totals =	$822.51		$904.0719	$904.08	$904.05	$904.10