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	$76.65	11.406%	$85.3927	$85.39	$85.40	$85.40
Purchase #2	$172.96	6.330%	$183.9084	$183.91	$183.90	$183.90
Purchase #3	$40.95	6.480%	$43.6036	$43.60	$43.60	$43.60
Purchase #4	$110.68	13.836%	$125.9937	$125.99	$126.00	$126.00
Purchase #5	$105.71	6.529%	$112.6118	$112.61	$112.60	$112.60
Purchase #6	$83.86	8.495%	$90.9839	$90.98	$91.00	$91.00
Purchase #7	$21.83	13.698%	$24.8203	$24.82	$24.80	$24.80
7 purchase totals =	$612.64		$667.3144	$667.30	$667.30	$667.30