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	$135.42	4.796%	$141.9147	$141.91	$141.90	$141.90
Purchase #2	$35.44	10.190%	$39.0513	$39.05	$39.05	$39.10
Purchase #3	$72.29	9.388%	$79.0766	$79.08	$79.10	$79.10
Purchase #4	$97.41	3.578%	$100.8953	$100.90	$100.90	$100.90
Purchase #5	$116.44	13.802%	$132.511	$132.51	$132.50	$132.50
Purchase #6	$117.86	11.834%	$131.8076	$131.81	$131.80	$131.80
Purchase #7	$43.65	7.433%	$46.8945	$46.89	$46.90	$46.90
7 purchase totals =	$618.51		$672.1510	$672.15	$672.15	$672.20