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	$210.69	13.629%	$239.4049	$239.40	$239.40	$239.40
Purchase #2	$146.70	3.541%	$151.8946	$151.89	$151.90	$151.90
Purchase #3	$84.92	5.528%	$89.6144	$89.61	$89.60	$89.60
Purchase #4	$80.42	4.283%	$83.8644	$83.86	$83.85	$83.90
Purchase #5	$91.49	8.811%	$99.5512	$99.55	$99.55	$99.60
Purchase #6	$32.49	10.514%	$35.906	$35.91	$35.90	$35.90
Purchase #7	$248.91	9.747%	$273.1713	$273.17	$273.15	$273.20
7 purchase totals =	$895.62		$973.4068	$973.39	$973.35	$973.50