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	$64.85	6.623%	$69.145	$69.15	$69.15	$69.10
Purchase #2	$123.40	6.161%	$131.0027	$131.00	$131.00	$131.00
Purchase #3	$39.83	13.828%	$45.3377	$45.34	$45.35	$45.30
Purchase #4	$185.63	10.228%	$204.6162	$204.62	$204.60	$204.60
Purchase #5	$112.31	4.155%	$116.9765	$116.98	$117.00	$117.00
Purchase #6	$53.87	5.703%	$56.9422	$56.94	$56.95	$56.90
Purchase #7	$89.54	10.440%	$98.888	$98.89	$98.90	$98.90
7 purchase totals =	$669.43		$722.9083	$722.92	$722.95	$722.80