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	$119.90	12.181%	$134.505	$134.51	$134.50	$134.50
Purchase #2	$169.49	8.753%	$184.3255	$184.33	$184.35	$184.30
Purchase #3	$28.47	13.258%	$32.2446	$32.24	$32.25	$32.20
Purchase #4	$130.42	5.256%	$137.2749	$137.27	$137.25	$137.30
Purchase #5	$72.89	11.612%	$81.354	$81.35	$81.35	$81.40
Purchase #6	$216.95	8.826%	$236.098	$236.10	$236.10	$236.10
Purchase #7	$163.47	5.665%	$172.7306	$172.73	$172.75	$172.70
7 purchase totals =	$901.59		$978.5326	$978.53	$978.55	$978.50