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	$33.84	11.237%	$37.6426	$37.64	$37.65	$37.60
Purchase #2	$150.80	5.290%	$158.7773	$158.78	$158.80	$158.80
Purchase #3	$152.29	12.162%	$170.8115	$170.81	$170.80	$170.80
Purchase #4	$78.86	13.568%	$89.5597	$89.56	$89.55	$89.60
Purchase #5	$225.46	8.372%	$244.3355	$244.34	$244.35	$244.30
Purchase #6	$181.87	13.254%	$205.975	$205.98	$206.00	$206.00
Purchase #7	$9.78	5.334%	$10.3017	$10.30	$10.30	$10.30
7 purchase totals =	$832.90		$917.4033	$917.41	$917.45	$917.40