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	$93.91	4.574%	$98.2054	$98.21	$98.20	$98.20
Purchase #2	$230.29	4.681%	$241.0699	$241.07	$241.05	$241.10
Purchase #3	$82.91	8.329%	$89.8156	$89.82	$89.80	$89.80
Purchase #4	$30.57	6.374%	$32.5185	$32.52	$32.50	$32.50
Purchase #5	$182.68	12.405%	$205.3415	$205.34	$205.35	$205.30
Purchase #6	$54.55	11.381%	$60.7583	$60.76	$60.75	$60.80
Purchase #7	$59.80	3.109%	$61.6592	$61.66	$61.65	$61.70
7 purchase totals =	$734.71		$789.3684	$789.38	$789.30	$789.40