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	$73.30	6.538%	$78.0924	$78.09	$78.10	$78.10
Purchase #2	$115.57	10.304%	$127.4783	$127.48	$127.50	$127.50
Purchase #3	$124.67	12.278%	$139.977	$139.98	$140.00	$140.00
Purchase #4	$151.67	10.809%	$168.064	$168.06	$168.05	$168.10
Purchase #5	$74.25	9.824%	$81.5443	$81.54	$81.55	$81.50
Purchase #6	$194.86	12.857%	$219.9132	$219.91	$219.90	$219.90
Purchase #7	$37.69	4.862%	$39.5225	$39.52	$39.50	$39.50
7 purchase totals =	$772.01		$854.5917	$854.58	$854.60	$854.60