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	$80.82	11.437%	$90.0634	$90.06	$90.05	$90.10
Purchase #2	$81.29	8.250%	$87.9964	$88.00	$88.00	$88.00
Purchase #3	$128.68	4.379%	$134.3149	$134.31	$134.30	$134.30
Purchase #4	$250.37	3.762%	$259.7889	$259.79	$259.80	$259.80
Purchase #5	$241.34	11.767%	$269.7385	$269.74	$269.75	$269.70
Purchase #6	$79.76	3.451%	$82.5125	$82.51	$82.50	$82.50
Purchase #7	$187.33	6.491%	$199.4896	$199.49	$199.50	$199.50
7 purchase totals =	$1,049.59		$1,123.9042	$1,123.90	$1,123.90	$1,123.90