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	$16.97	3.159%	$17.5061	$17.51	$17.50	$17.50
Purchase #2	$31.96	3.748%	$33.1579	$33.16	$33.15	$33.20
Purchase #3	$80.97	11.426%	$90.2216	$90.22	$90.20	$90.20
Purchase #4	$127.39	4.651%	$133.3149	$133.31	$133.30	$133.30
Purchase #5	$249.83	3.427%	$258.3917	$258.39	$258.40	$258.40
Purchase #6	$143.29	10.112%	$157.7795	$157.78	$157.80	$157.80
Purchase #7	$86.63	6.820%	$92.5382	$92.54	$92.55	$92.50
7 purchase totals =	$737.04		$782.9099	$782.91	$782.90	$782.90