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	$38.82	10.679%	$42.9656	$42.97	$42.95	$43.00
Purchase #2	$207.75	11.307%	$231.2403	$231.24	$231.25	$231.20
Purchase #3	$82.61	4.609%	$86.4175	$86.42	$86.40	$86.40
Purchase #4	$16.61	12.305%	$18.6539	$18.65	$18.65	$18.70
Purchase #5	$90.68	10.690%	$100.3737	$100.37	$100.35	$100.40
Purchase #6	$96.34	11.354%	$107.2784	$107.28	$107.30	$107.30
Purchase #7	$216.47	6.753%	$231.0882	$231.09	$231.10	$231.10
7 purchase totals =	$749.28		$818.0176	$818.02	$818.00	$818.10