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	$73.93	9.451%	$80.9171	$80.92	$80.90	$80.90
Purchase #2	$78.96	13.752%	$89.8186	$89.82	$89.80	$89.80
Purchase #3	$132.34	3.525%	$137.005	$137.01	$137.00	$137.00
Purchase #4	$169.49	13.360%	$192.1339	$192.13	$192.15	$192.10
Purchase #5	$240.99	4.164%	$251.0248	$251.02	$251.00	$251.00
Purchase #6	$223.81	11.462%	$249.4631	$249.46	$249.45	$249.50
Purchase #7	$140.57	4.280%	$146.5864	$146.59	$146.60	$146.60
7 purchase totals =	$1,060.09		$1,146.9489	$1,146.95	$1,146.90	$1,146.90