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	$9.78	11.277%	$10.8829	$10.88	$10.90	$10.90
Purchase #2	$168.38	6.586%	$179.4695	$179.47	$179.45	$179.50
Purchase #3	$85.94	10.688%	$95.1253	$95.13	$95.15	$95.10
Purchase #4	$168.79	9.174%	$184.2748	$184.27	$184.25	$184.30
Purchase #5	$137.27	9.171%	$149.859	$149.86	$149.85	$149.90
Purchase #6	$68.79	3.155%	$70.9603	$70.96	$70.95	$71.00
Purchase #7	$88.70	12.151%	$99.4779	$99.48	$99.50	$99.50
7 purchase totals =	$727.65		$790.0497	$790.05	$790.05	$790.20