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	$48.95	5.846%	$51.8116	$51.81	$51.80	$51.80
Purchase #2	$173.89	13.126%	$196.7148	$196.71	$196.70	$196.70
Purchase #3	$87.71	6.764%	$93.6427	$93.64	$93.65	$93.60
Purchase #4	$111.63	3.363%	$115.3841	$115.38	$115.40	$115.40
Purchase #5	$82.29	4.540%	$86.026	$86.03	$86.05	$86.00
Purchase #6	$16.90	10.565%	$18.6855	$18.69	$18.70	$18.70
Purchase #7	$41.67	8.508%	$45.2153	$45.22	$45.20	$45.20
7 purchase totals =	$563.04		$607.4800	$607.48	$607.50	$607.40