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	$27.28	13.719%	$31.0225	$31.02	$31.00	$31.00
Purchase #2	$130.54	8.562%	$141.7168	$141.72	$141.70	$141.70
Purchase #3	$135.55	3.118%	$139.7764	$139.78	$139.80	$139.80
Purchase #4	$90.89	5.563%	$95.9462	$95.95	$95.95	$95.90
Purchase #5	$14.53	7.358%	$15.5991	$15.60	$15.60	$15.60
Purchase #6	$144.35	8.222%	$156.2185	$156.22	$156.20	$156.20
Purchase #7	$91.31	8.443%	$99.0193	$99.02	$99.00	$99.00
7 purchase totals =	$634.45		$679.2988	$679.31	$679.25	$679.20