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	$79.34	13.342%	$89.9255	$89.93	$89.95	$89.90
Purchase #2	$123.55	11.596%	$137.8769	$137.88	$137.90	$137.90
Purchase #3	$147.56	3.320%	$152.459	$152.46	$152.45	$152.50
Purchase #4	$40.93	10.842%	$45.3676	$45.37	$45.35	$45.40
Purchase #5	$175.65	9.532%	$192.393	$192.39	$192.40	$192.40
Purchase #6	$66.79	10.257%	$73.6407	$73.64	$73.65	$73.60
Purchase #7	$43.99	5.480%	$46.4007	$46.40	$46.40	$46.40
7 purchase totals =	$677.81		$738.0634	$738.07	$738.10	$738.10