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	$158.46	6.758%	$169.1687	$169.17	$169.15	$169.20
Purchase #2	$93.97	12.680%	$105.8854	$105.89	$105.90	$105.90
Purchase #3	$112.51	10.569%	$124.4012	$124.40	$124.40	$124.40
Purchase #4	$80.99	12.274%	$90.9307	$90.93	$90.95	$90.90
Purchase #5	$72.60	10.146%	$79.966	$79.97	$79.95	$80.00
Purchase #6	$38.55	9.479%	$42.2042	$42.20	$42.20	$42.20
Purchase #7	$88.69	12.577%	$99.8445	$99.84	$99.85	$99.80
7 purchase totals =	$645.77		$712.4007	$712.40	$712.40	$712.40