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	$129.31	3.539%	$133.8863	$133.89	$133.90	$133.90
Purchase #2	$38.53	4.230%	$40.1598	$40.16	$40.15	$40.20
Purchase #3	$55.58	10.799%	$61.5821	$61.58	$61.60	$61.60
Purchase #4	$155.65	6.284%	$165.431	$165.43	$165.45	$165.40
Purchase #5	$250.90	11.591%	$279.9818	$279.98	$280.00	$280.00
Purchase #6	$169.35	3.269%	$174.8861	$174.89	$174.90	$174.90
Purchase #7	$214.39	5.102%	$225.3282	$225.33	$225.35	$225.30
7 purchase totals =	$1,013.71		$1,081.2553	$1,081.26	$1,081.35	$1,081.30