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	$120.81	5.616%	$127.5947	$127.59	$127.60	$127.60
Purchase #2	$51.51	8.871%	$56.0795	$56.08	$56.10	$56.10
Purchase #3	$39.68	4.801%	$41.585	$41.59	$41.60	$41.60
Purchase #4	$237.37	3.503%	$245.6851	$245.69	$245.70	$245.70
Purchase #5	$203.74	10.327%	$224.7802	$224.78	$224.80	$224.80
Purchase #6	$242.42	8.705%	$263.5227	$263.52	$263.50	$263.50
Purchase #7	$124.52	6.340%	$132.4146	$132.41	$132.40	$132.40
7 purchase totals =	$1,020.05		$1,091.6618	$1,091.66	$1,091.70	$1,091.70