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	$106.53	7.786%	$114.8244	$114.82	$114.80	$114.80
Purchase #2	$187.52	3.660%	$194.3832	$194.38	$194.40	$194.40
Purchase #3	$31.58	12.510%	$35.5307	$35.53	$35.55	$35.50
Purchase #4	$205.38	7.718%	$221.2312	$221.23	$221.25	$221.20
Purchase #5	$129.61	9.837%	$142.3597	$142.36	$142.35	$142.40
Purchase #6	$103.84	5.405%	$109.4526	$109.45	$109.45	$109.50
Purchase #7	$30.71	10.588%	$33.9616	$33.96	$33.95	$34.00
7 purchase totals =	$795.17		$851.7434	$851.73	$851.75	$851.80