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	$109.66	10.607%	$121.2916	$121.29	$121.30	$121.30
Purchase #2	$126.87	11.336%	$141.252	$141.25	$141.25	$141.30
Purchase #3	$10.52	9.587%	$11.5286	$11.53	$11.55	$11.50
Purchase #4	$66.54	7.357%	$71.4353	$71.44	$71.45	$71.40
Purchase #5	$191.32	9.783%	$210.0368	$210.04	$210.05	$210.00
Purchase #6	$62.94	11.397%	$70.1133	$70.11	$70.10	$70.10
Purchase #7	$158.69	6.154%	$168.4558	$168.46	$168.45	$168.50
7 purchase totals =	$726.54		$794.1134	$794.12	$794.15	$794.10