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	$248.26	4.572%	$259.6104	$259.61	$259.60	$259.60
Purchase #2	$82.39	11.596%	$91.9439	$91.94	$91.95	$91.90
Purchase #3	$104.35	7.693%	$112.3776	$112.38	$112.40	$112.40
Purchase #4	$242.60	11.266%	$269.9313	$269.93	$269.95	$269.90
Purchase #5	$26.93	4.478%	$28.1359	$28.14	$28.15	$28.10
Purchase #6	$161.43	10.462%	$178.3188	$178.32	$178.30	$178.30
Purchase #7	$121.55	8.183%	$131.4964	$131.50	$131.50	$131.50
7 purchase totals =	$987.51		$1,071.8143	$1,071.82	$1,071.85	$1,071.70