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	$95.97	3.593%	$99.4182	$99.42	$99.40	$99.40
Purchase #2	$113.43	13.261%	$128.472	$128.47	$128.45	$128.50
Purchase #3	$139.34	9.585%	$152.6957	$152.70	$152.70	$152.70
Purchase #4	$78.69	6.264%	$83.6191	$83.62	$83.60	$83.60
Purchase #5	$42.41	10.314%	$46.7842	$46.78	$46.80	$46.80
Purchase #6	$200.66	9.745%	$220.2143	$220.21	$220.20	$220.20
Purchase #7	$39.38	5.452%	$41.527	$41.53	$41.55	$41.50
7 purchase totals =	$709.88		$772.7305	$772.73	$772.70	$772.70