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	$110.34	5.582%	$116.4992	$116.50	$116.50	$116.50
Purchase #2	$183.91	3.727%	$190.7643	$190.76	$190.75	$190.80
Purchase #3	$55.68	6.113%	$59.0837	$59.08	$59.10	$59.10
Purchase #4	$96.81	4.113%	$100.7918	$100.79	$100.80	$100.80
Purchase #5	$72.43	11.437%	$80.7138	$80.71	$80.70	$80.70
Purchase #6	$187.38	8.773%	$203.8188	$203.82	$203.80	$203.80
Purchase #7	$143.92	11.354%	$160.2607	$160.26	$160.25	$160.30
7 purchase totals =	$850.47		$911.9323	$911.92	$911.90	$912.00