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	$101.96	3.666%	$105.6979	$105.70	$105.70	$105.70
Purchase #2	$144.91	10.565%	$160.2197	$160.22	$160.20	$160.20
Purchase #3	$107.62	8.247%	$116.4954	$116.50	$116.50	$116.50
Purchase #4	$95.40	8.834%	$103.8276	$103.83	$103.85	$103.80
Purchase #5	$222.39	6.592%	$237.0499	$237.05	$237.05	$237.00
Purchase #6	$30.89	6.512%	$32.9016	$32.90	$32.90	$32.90
Purchase #7	$55.31	9.359%	$60.4865	$60.49	$60.50	$60.50
7 purchase totals =	$758.48		$816.6786	$816.69	$816.70	$816.60