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	$28.28	10.543%	$31.2616	$31.26	$31.25	$31.30
Purchase #2	$239.48	8.603%	$260.0825	$260.08	$260.10	$260.10
Purchase #3	$12.75	11.769%	$14.2505	$14.25	$14.25	$14.30
Purchase #4	$55.85	6.868%	$59.6858	$59.69	$59.70	$59.70
Purchase #5	$148.90	7.868%	$160.6155	$160.62	$160.60	$160.60
Purchase #6	$53.30	11.648%	$59.5084	$59.51	$59.50	$59.50
Purchase #7	$142.95	8.794%	$155.521	$155.52	$155.50	$155.50
7 purchase totals =	$681.51		$740.9253	$740.93	$740.90	$741.00