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	$136.55	4.456%	$142.6347	$142.63	$142.65	$142.60
Purchase #2	$67.87	13.223%	$76.8445	$76.84	$76.85	$76.80
Purchase #3	$20.33	4.186%	$21.181	$21.18	$21.20	$21.20
Purchase #4	$129.79	3.737%	$134.6403	$134.64	$134.65	$134.60
Purchase #5	$50.78	7.386%	$54.5306	$54.53	$54.55	$54.50
Purchase #6	$211.73	9.231%	$231.2748	$231.27	$231.25	$231.30
Purchase #7	$5.49	12.188%	$6.1591	$6.16	$6.15	$6.20
7 purchase totals =	$622.54		$667.2650	$667.25	$667.30	$667.20