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	$18.25	13.786%	$20.7659	$20.77	$20.75	$20.80
Purchase #2	$99.68	13.280%	$112.9175	$112.92	$112.90	$112.90
Purchase #3	$133.51	7.373%	$143.3537	$143.35	$143.35	$143.40
Purchase #4	$186.60	12.480%	$209.8877	$209.89	$209.90	$209.90
Purchase #5	$197.43	7.116%	$211.4791	$211.48	$211.50	$211.50
Purchase #6	$200.99	11.434%	$223.9712	$223.97	$223.95	$224.00
Purchase #7	$28.81	12.615%	$32.4444	$32.44	$32.45	$32.40
7 purchase totals =	$865.27		$954.8195	$954.82	$954.80	$954.90