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	$33.97	12.650%	$38.2672	$38.27	$38.25	$38.30
Purchase #2	$96.64	13.646%	$109.8275	$109.83	$109.85	$109.80
Purchase #3	$229.30	6.221%	$243.5648	$243.56	$243.55	$243.60
Purchase #4	$241.65	4.763%	$253.1598	$253.16	$253.15	$253.20
Purchase #5	$14.61	13.140%	$16.5298	$16.53	$16.55	$16.50
Purchase #6	$127.47	3.512%	$131.9467	$131.95	$131.95	$131.90
Purchase #7	$156.35	3.756%	$162.2225	$162.22	$162.20	$162.20
7 purchase totals =	$899.99		$955.5183	$955.52	$955.50	$955.50