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	$46.89	3.604%	$48.5799	$48.58	$48.60	$48.60
Purchase #2	$213.37	13.228%	$241.5946	$241.59	$241.60	$241.60
Purchase #3	$172.97	12.280%	$194.2107	$194.21	$194.20	$194.20
Purchase #4	$151.44	5.610%	$159.9358	$159.94	$159.95	$159.90
Purchase #5	$105.27	4.148%	$109.6366	$109.64	$109.65	$109.60
Purchase #6	$224.47	7.533%	$241.3793	$241.38	$241.40	$241.40
Purchase #7	$213.71	4.257%	$222.8076	$222.81	$222.80	$222.80
7 purchase totals =	$1,128.12		$1,218.1445	$1,218.15	$1,218.20	$1,218.10