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	$113.48	3.381%	$117.3168	$117.32	$117.30	$117.30
Purchase #2	$34.27	8.810%	$37.2892	$37.29	$37.30	$37.30
Purchase #3	$190.90	11.539%	$212.928	$212.93	$212.95	$212.90
Purchase #4	$221.48	8.735%	$240.8263	$240.83	$240.85	$240.80
Purchase #5	$240.90	3.474%	$249.2689	$249.27	$249.25	$249.30
Purchase #6	$49.92	8.722%	$54.274	$54.27	$54.25	$54.30
Purchase #7	$211.85	8.744%	$230.3742	$230.37	$230.35	$230.40
7 purchase totals =	$1,062.80		$1,142.2774	$1,142.28	$1,142.25	$1,142.30