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	$222.85	9.278%	$243.526	$243.53	$243.55	$243.50
Purchase #2	$198.31	9.321%	$216.7945	$216.79	$216.80	$216.80
Purchase #3	$238.37	8.372%	$258.3263	$258.33	$258.35	$258.30
Purchase #4	$77.83	13.707%	$88.4982	$88.50	$88.50	$88.50
Purchase #5	$250.41	12.103%	$280.7171	$280.72	$280.70	$280.70
Purchase #6	$30.67	10.699%	$33.9514	$33.95	$33.95	$34.00
Purchase #7	$99.48	12.765%	$112.1786	$112.18	$112.20	$112.20
7 purchase totals =	$1,117.92		$1,233.9921	$1,234.00	$1,234.05	$1,234.00