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	$20.43	6.248%	$21.7065	$21.71	$21.70	$21.70
Purchase #2	$81.28	6.491%	$86.5559	$86.56	$86.55	$86.60
Purchase #3	$95.30	12.574%	$107.283	$107.28	$107.30	$107.30
Purchase #4	$153.34	7.410%	$164.7025	$164.70	$164.70	$164.70
Purchase #5	$155.69	8.364%	$168.7119	$168.71	$168.70	$168.70
Purchase #6	$89.46	10.787%	$99.1101	$99.11	$99.10	$99.10
Purchase #7	$18.29	11.683%	$20.4268	$20.43	$20.45	$20.40
7 purchase totals =	$613.79		$668.4967	$668.50	$668.50	$668.50