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	$53.62	4.236%	$55.8913	$55.89	$55.90	$55.90
Purchase #2	$191.90	3.745%	$199.0867	$199.09	$199.10	$199.10
Purchase #3	$104.66	5.315%	$110.2227	$110.22	$110.20	$110.20
Purchase #4	$118.39	11.142%	$131.581	$131.58	$131.60	$131.60
Purchase #5	$93.51	10.157%	$103.0078	$103.01	$103.00	$103.00
Purchase #6	$246.55	8.540%	$267.6054	$267.61	$267.60	$267.60
Purchase #7	$239.48	6.827%	$255.8293	$255.83	$255.85	$255.80
7 purchase totals =	$1,048.11		$1,123.2242	$1,123.23	$1,123.25	$1,123.20