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	$145.56	6.664%	$155.2601	$155.26	$155.25	$155.30
Purchase #2	$182.76	4.186%	$190.4103	$190.41	$190.40	$190.40
Purchase #3	$19.29	4.446%	$20.1476	$20.15	$20.15	$20.10
Purchase #4	$134.38	3.417%	$138.9718	$138.97	$138.95	$139.00
Purchase #5	$165.48	4.444%	$172.8339	$172.83	$172.85	$172.80
Purchase #6	$100.62	10.442%	$111.1267	$111.13	$111.15	$111.10
Purchase #7	$180.76	10.760%	$200.2098	$200.21	$200.20	$200.20
7 purchase totals =	$928.85		$988.9602	$988.96	$988.95	$988.90