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	$63.50	13.147%	$71.8483	$71.85	$71.85	$71.80
Purchase #2	$131.72	7.501%	$141.6003	$141.60	$141.60	$141.60
Purchase #3	$31.35	6.164%	$33.2824	$33.28	$33.30	$33.30
Purchase #4	$248.83	7.871%	$268.4154	$268.42	$268.40	$268.40
Purchase #5	$209.64	9.678%	$229.929	$229.93	$229.95	$229.90
Purchase #6	$184.25	5.741%	$194.8278	$194.83	$194.85	$194.80
Purchase #7	$45.46	12.460%	$51.1243	$51.12	$51.10	$51.10
7 purchase totals =	$914.75		$991.0275	$991.03	$991.05	$990.90