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	$28.98	11.592%	$32.3394	$32.34	$32.35	$32.30
Purchase #2	$198.45	8.619%	$215.5544	$215.55	$215.55	$215.60
Purchase #3	$91.84	3.297%	$94.868	$94.87	$94.85	$94.90
Purchase #4	$176.52	11.367%	$196.585	$196.59	$196.60	$196.60
Purchase #5	$233.55	7.366%	$250.7533	$250.75	$250.75	$250.80
Purchase #6	$126.39	7.601%	$135.9969	$136.00	$136.00	$136.00
Purchase #7	$196.89	9.363%	$215.3248	$215.32	$215.30	$215.30
7 purchase totals =	$1,052.62		$1,141.4218	$1,141.42	$1,141.40	$1,141.50