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	$53.85	5.827%	$56.9878	$56.99	$57.00	$57.00
Purchase #2	$200.33	9.229%	$218.8185	$218.82	$218.80	$218.80
Purchase #3	$136.70	10.868%	$151.5566	$151.56	$151.55	$151.60
Purchase #4	$164.78	12.848%	$185.9509	$185.95	$185.95	$186.00
Purchase #5	$123.73	6.711%	$132.0335	$132.03	$132.05	$132.00
Purchase #6	$34.74	7.463%	$37.3326	$37.33	$37.35	$37.30
Purchase #7	$185.49	5.647%	$195.9646	$195.96	$195.95	$196.00
7 purchase totals =	$899.62		$978.6445	$978.64	$978.65	$978.70