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	$219.30	13.486%	$248.8748	$248.87	$248.85	$248.90
Purchase #2	$220.59	8.276%	$238.846	$238.85	$238.85	$238.80
Purchase #3	$97.25	8.844%	$105.8508	$105.85	$105.85	$105.90
Purchase #4	$81.55	9.618%	$89.3935	$89.39	$89.40	$89.40
Purchase #5	$162.86	10.364%	$179.7388	$179.74	$179.75	$179.70
Purchase #6	$96.59	8.539%	$104.8378	$104.84	$104.85	$104.80
Purchase #7	$15.31	7.120%	$16.4001	$16.40	$16.40	$16.40
7 purchase totals =	$893.45		$983.9418	$983.94	$983.95	$983.90