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	$189.84	10.311%	$209.4144	$209.41	$209.40	$209.40
Purchase #2	$136.65	6.301%	$145.2603	$145.26	$145.25	$145.30
Purchase #3	$80.54	13.427%	$91.3541	$91.35	$91.35	$91.40
Purchase #4	$11.50	4.537%	$12.0218	$12.02	$12.00	$12.00
Purchase #5	$131.79	4.633%	$137.8958	$137.90	$137.90	$137.90
Purchase #6	$198.31	5.151%	$208.5249	$208.52	$208.50	$208.50
Purchase #7	$17.69	3.472%	$18.3042	$18.30	$18.30	$18.30
7 purchase totals =	$766.32		$822.7755	$822.76	$822.70	$822.80