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	$52.72	4.679%	$55.1868	$55.19	$55.20	$55.20
Purchase #2	$129.55	3.540%	$134.1361	$134.14	$134.15	$134.10
Purchase #3	$189.82	4.355%	$198.0867	$198.09	$198.10	$198.10
Purchase #4	$146.59	10.851%	$162.4965	$162.50	$162.50	$162.50
Purchase #5	$83.39	11.374%	$92.8748	$92.87	$92.85	$92.90
Purchase #6	$147.93	13.305%	$167.6121	$167.61	$167.60	$167.60
Purchase #7	$100.41	3.538%	$103.9625	$103.96	$103.95	$104.00
7 purchase totals =	$850.41		$914.3555	$914.36	$914.35	$914.40