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	$78.64	6.146%	$83.4732	$83.47	$83.45	$83.50
Purchase #2	$142.65	11.431%	$158.9563	$158.96	$158.95	$159.00
Purchase #3	$148.71	3.869%	$154.4636	$154.46	$154.45	$154.50
Purchase #4	$105.93	7.391%	$113.7593	$113.76	$113.75	$113.80
Purchase #5	$127.80	9.219%	$139.5819	$139.58	$139.60	$139.60
Purchase #6	$136.46	11.562%	$152.2375	$152.24	$152.25	$152.20
Purchase #7	$64.44	5.281%	$67.8431	$67.84	$67.85	$67.80
7 purchase totals =	$804.63		$870.3149	$870.31	$870.30	$870.40