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	$84.89	6.225%	$90.1744	$90.17	$90.15	$90.20
Purchase #2	$169.68	12.151%	$190.2978	$190.30	$190.30	$190.30
Purchase #3	$224.59	7.167%	$240.6864	$240.69	$240.70	$240.70
Purchase #4	$126.98	3.103%	$130.9202	$130.92	$130.90	$130.90
Purchase #5	$79.37	4.739%	$83.1313	$83.13	$83.15	$83.10
Purchase #6	$201.43	13.195%	$228.0087	$228.01	$228.00	$228.00
Purchase #7	$71.35	12.502%	$80.2702	$80.27	$80.25	$80.30
7 purchase totals =	$958.29		$1,043.4890	$1,043.49	$1,043.45	$1,043.50