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	$169.79	6.173%	$180.2711	$180.27	$180.25	$180.30
Purchase #2	$180.69	8.810%	$196.6088	$196.61	$196.60	$196.60
Purchase #3	$105.51	12.750%	$118.9625	$118.96	$118.95	$119.00
Purchase #4	$207.74	7.790%	$223.9229	$223.92	$223.90	$223.90
Purchase #5	$36.83	5.151%	$38.7271	$38.73	$38.75	$38.70
Purchase #6	$209.90	9.550%	$229.9455	$229.95	$229.95	$229.90
Purchase #7	$154.82	12.422%	$174.0517	$174.05	$174.05	$174.10
7 purchase totals =	$1,065.28		$1,162.4896	$1,162.49	$1,162.45	$1,162.50