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	$86.92	5.153%	$91.399	$91.40	$91.40	$91.40
Purchase #2	$93.94	6.701%	$100.2349	$100.23	$100.25	$100.20
Purchase #3	$13.83	7.636%	$14.8861	$14.89	$14.90	$14.90
Purchase #4	$74.56	10.660%	$82.5081	$82.51	$82.50	$82.50
Purchase #5	$18.44	9.411%	$20.1754	$20.18	$20.20	$20.20
Purchase #6	$155.57	8.513%	$168.8137	$168.81	$168.80	$168.80
Purchase #7	$140.94	13.552%	$160.0402	$160.04	$160.05	$160.00
7 purchase totals =	$584.20		$638.0574	$638.06	$638.10	$638.00