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	$52.97	12.736%	$59.7163	$59.72	$59.70	$59.70
Purchase #2	$75.99	5.583%	$80.2325	$80.23	$80.25	$80.20
Purchase #3	$174.99	6.694%	$186.7038	$186.70	$186.70	$186.70
Purchase #4	$78.33	5.308%	$82.4878	$82.49	$82.50	$82.50
Purchase #5	$45.41	5.843%	$48.0633	$48.06	$48.05	$48.10
Purchase #6	$81.62	9.282%	$89.196	$89.20	$89.20	$89.20
Purchase #7	$42.38	6.178%	$44.9982	$45.00	$45.00	$45.00
7 purchase totals =	$551.69		$591.3979	$591.40	$591.40	$591.40