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	$50.72	10.758%	$56.1765	$56.18	$56.20	$56.20
Purchase #2	$118.93	3.709%	$123.3411	$123.34	$123.35	$123.30
Purchase #3	$140.61	9.200%	$153.5461	$153.55	$153.55	$153.50
Purchase #4	$85.85	7.361%	$92.1694	$92.17	$92.15	$92.20
Purchase #5	$152.25	5.227%	$160.2081	$160.21	$160.20	$160.20
Purchase #6	$221.81	11.113%	$246.4597	$246.46	$246.45	$246.50
Purchase #7	$11.41	12.311%	$12.8147	$12.81	$12.80	$12.80
7 purchase totals =	$781.58		$844.7156	$844.72	$844.70	$844.70