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	$28.96	11.704%	$32.3495	$32.35	$32.35	$32.30
Purchase #2	$207.44	5.667%	$219.1956	$219.20	$219.20	$219.20
Purchase #3	$238.85	7.585%	$256.9668	$256.97	$256.95	$257.00
Purchase #4	$56.27	6.431%	$59.8887	$59.89	$59.90	$59.90
Purchase #5	$115.34	11.204%	$128.2627	$128.26	$128.25	$128.30
Purchase #6	$217.53	12.771%	$245.3108	$245.31	$245.30	$245.30
Purchase #7	$30.43	11.541%	$33.9419	$33.94	$33.95	$33.90
7 purchase totals =	$894.82		$975.9160	$975.92	$975.90	$975.90