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	$116.42	8.671%	$126.5148	$126.51	$126.50	$126.50
Purchase #2	$78.89	13.228%	$89.3256	$89.33	$89.35	$89.30
Purchase #3	$62.35	13.118%	$70.5291	$70.53	$70.55	$70.50
Purchase #4	$19.42	8.624%	$21.0948	$21.09	$21.10	$21.10
Purchase #5	$162.97	5.331%	$171.6579	$171.66	$171.65	$171.70
Purchase #6	$200.81	4.735%	$210.3184	$210.32	$210.30	$210.30
Purchase #7	$82.68	6.744%	$88.2559	$88.26	$88.25	$88.30
7 purchase totals =	$723.54		$777.6965	$777.70	$777.70	$777.70