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	$15.66	7.404%	$16.8195	$16.82	$16.80	$16.80
Purchase #2	$76.82	3.361%	$79.4019	$79.40	$79.40	$79.40
Purchase #3	$52.49	13.155%	$59.3951	$59.40	$59.40	$59.40
Purchase #4	$31.97	4.825%	$33.5126	$33.51	$33.50	$33.50
Purchase #5	$210.38	10.623%	$232.7287	$232.73	$232.75	$232.70
Purchase #6	$33.53	11.827%	$37.4956	$37.50	$37.50	$37.50
Purchase #7	$174.65	4.726%	$182.904	$182.90	$182.90	$182.90
7 purchase totals =	$595.50		$642.2574	$642.26	$642.25	$642.20