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	$29.90	8.798%	$32.5306	$32.53	$32.55	$32.50
Purchase #2	$120.92	13.598%	$137.3627	$137.36	$137.35	$137.40
Purchase #3	$96.48	9.176%	$105.333	$105.33	$105.35	$105.30
Purchase #4	$168.61	4.575%	$176.3239	$176.32	$176.30	$176.30
Purchase #5	$227.83	4.721%	$238.5859	$238.59	$238.60	$238.60
Purchase #6	$130.88	8.441%	$141.9276	$141.93	$141.95	$141.90
Purchase #7	$215.64	10.440%	$238.1528	$238.15	$238.15	$238.20
7 purchase totals =	$990.26		$1,070.2165	$1,070.21	$1,070.25	$1,070.20