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	$133.54	9.306%	$145.9672	$145.97	$145.95	$146.00
Purchase #2	$206.91	8.186%	$223.8477	$223.85	$223.85	$223.80
Purchase #3	$75.72	13.179%	$85.6991	$85.70	$85.70	$85.70
Purchase #4	$111.38	3.154%	$114.8929	$114.89	$114.90	$114.90
Purchase #5	$209.98	12.181%	$235.5577	$235.56	$235.55	$235.60
Purchase #6	$36.77	9.382%	$40.2198	$40.22	$40.20	$40.20
Purchase #7	$12.87	5.600%	$13.5907	$13.59	$13.60	$13.60
7 purchase totals =	$787.17		$859.7751	$859.78	$859.75	$859.80