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	$97.88	3.106%	$100.9202	$100.92	$100.90	$100.90
Purchase #2	$246.90	8.349%	$267.5137	$267.51	$267.50	$267.50
Purchase #3	$13.90	7.155%	$14.8945	$14.89	$14.90	$14.90
Purchase #4	$247.70	10.224%	$273.0248	$273.02	$273.00	$273.00
Purchase #5	$10.30	4.139%	$10.7263	$10.73	$10.75	$10.70
Purchase #6	$42.75	9.512%	$46.8164	$46.82	$46.80	$46.80
Purchase #7	$151.55	13.304%	$171.7122	$171.71	$171.70	$171.70
7 purchase totals =	$810.98		$885.6081	$885.60	$885.55	$885.50