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	$53.44	6.245%	$56.7773	$56.78	$56.80	$56.80
Purchase #2	$33.96	12.662%	$38.26	$38.26	$38.25	$38.30
Purchase #3	$82.49	4.766%	$86.4215	$86.42	$86.40	$86.40
Purchase #4	$107.92	3.375%	$111.5623	$111.56	$111.55	$111.60
Purchase #5	$150.69	5.291%	$158.663	$158.66	$158.65	$158.70
Purchase #6	$148.27	6.112%	$157.3323	$157.33	$157.35	$157.30
Purchase #7	$249.82	8.440%	$270.9048	$270.90	$270.90	$270.90
7 purchase totals =	$826.59		$879.9212	$879.91	$879.90	$880.00