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	$28.38	12.650%	$31.9701	$31.97	$31.95	$32.00
Purchase #2	$94.38	6.571%	$100.5817	$100.58	$100.60	$100.60
Purchase #3	$95.40	4.820%	$99.9983	$100.00	$100.00	$100.00
Purchase #4	$165.92	4.658%	$173.6486	$173.65	$173.65	$173.60
Purchase #5	$23.87	8.179%	$25.8223	$25.82	$25.80	$25.80
Purchase #6	$165.65	12.671%	$186.6395	$186.64	$186.65	$186.60
Purchase #7	$18.89	5.430%	$19.9157	$19.92	$19.90	$19.90
7 purchase totals =	$592.49		$638.5762	$638.58	$638.55	$638.50