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	$193.52	10.402%	$213.65	$213.65	$213.65	$213.70
Purchase #2	$133.29	13.199%	$150.8829	$150.88	$150.90	$150.90
Purchase #3	$84.77	5.680%	$89.5849	$89.58	$89.60	$89.60
Purchase #4	$114.66	10.669%	$126.8931	$126.89	$126.90	$126.90
Purchase #5	$84.73	12.369%	$95.2103	$95.21	$95.20	$95.20
Purchase #6	$123.48	7.422%	$132.6447	$132.64	$132.65	$132.60
Purchase #7	$55.62	6.665%	$59.3271	$59.33	$59.35	$59.30
7 purchase totals =	$790.07		$868.1930	$868.18	$868.25	$868.20