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	$135.88	3.454%	$140.5733	$140.57	$140.55	$140.60
Purchase #2	$191.76	7.255%	$205.6722	$205.67	$205.65	$205.70
Purchase #3	$209.63	4.661%	$219.4009	$219.40	$219.40	$219.40
Purchase #4	$16.77	11.566%	$18.7096	$18.71	$18.70	$18.70
Purchase #5	$96.70	3.608%	$100.1889	$100.19	$100.20	$100.20
Purchase #6	$78.50	5.431%	$82.7633	$82.76	$82.75	$82.80
Purchase #7	$50.85	3.192%	$52.4731	$52.47	$52.45	$52.50
7 purchase totals =	$780.09		$819.7813	$819.77	$819.70	$819.90