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	$158.77	12.527%	$178.6591	$178.66	$178.65	$178.70
Purchase #2	$115.69	3.285%	$119.4904	$119.49	$119.50	$119.50
Purchase #3	$39.93	9.705%	$43.8052	$43.81	$43.80	$43.80
Purchase #4	$142.91	12.627%	$160.9552	$160.96	$160.95	$161.00
Purchase #5	$31.64	5.302%	$33.3176	$33.32	$33.30	$33.30
Purchase #6	$167.45	10.707%	$185.3789	$185.38	$185.40	$185.40
Purchase #7	$55.27	6.356%	$58.783	$58.78	$58.80	$58.80
7 purchase totals =	$711.66		$780.3894	$780.40	$780.40	$780.50