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	$32.38	13.591%	$36.7808	$36.78	$36.80	$36.80
Purchase #2	$113.97	7.284%	$122.2716	$122.27	$122.25	$122.30
Purchase #3	$90.68	3.679%	$94.0161	$94.02	$94.00	$94.00
Purchase #4	$151.65	13.644%	$172.3411	$172.34	$172.35	$172.30
Purchase #5	$129.53	13.685%	$147.2562	$147.26	$147.25	$147.30
Purchase #6	$57.90	5.773%	$61.2426	$61.24	$61.25	$61.20
Purchase #7	$182.60	7.518%	$196.3279	$196.33	$196.35	$196.30
7 purchase totals =	$758.71		$830.2363	$830.24	$830.25	$830.20