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	$12.29	10.654%	$13.5994	$13.60	$13.60	$13.60
Purchase #2	$244.92	6.196%	$260.0952	$260.10	$260.10	$260.10
Purchase #3	$168.49	6.794%	$179.9372	$179.94	$179.95	$179.90
Purchase #4	$97.90	11.194%	$108.8589	$108.86	$108.85	$108.90
Purchase #5	$56.97	4.234%	$59.3821	$59.38	$59.40	$59.40
Purchase #6	$88.88	13.542%	$100.9161	$100.92	$100.90	$100.90
Purchase #7	$188.32	3.112%	$194.1805	$194.18	$194.20	$194.20
7 purchase totals =	$857.77		$916.9694	$916.98	$917.00	$917.00