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	$121.65	7.740%	$131.0657	$131.07	$131.05	$131.10
Purchase #2	$204.78	8.195%	$221.5617	$221.56	$221.55	$221.60
Purchase #3	$95.88	9.691%	$105.1717	$105.17	$105.15	$105.20
Purchase #4	$95.69	4.384%	$99.885	$99.89	$99.90	$99.90
Purchase #5	$19.74	4.344%	$20.5975	$20.60	$20.60	$20.60
Purchase #6	$210.75	8.481%	$228.6237	$228.62	$228.60	$228.60
Purchase #7	$158.95	4.843%	$166.6479	$166.65	$166.65	$166.60
7 purchase totals =	$907.44		$973.5532	$973.56	$973.50	$973.60