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	$173.41	7.111%	$185.7412	$185.74	$185.75	$185.70
Purchase #2	$187.93	13.644%	$213.5712	$213.57	$213.55	$213.60
Purchase #3	$64.42	11.146%	$71.6003	$71.60	$71.60	$71.60
Purchase #4	$77.31	10.247%	$85.232	$85.23	$85.25	$85.20
Purchase #5	$77.79	11.727%	$86.9124	$86.91	$86.90	$86.90
Purchase #6	$40.41	11.212%	$44.9408	$44.94	$44.95	$44.90
Purchase #7	$98.31	13.364%	$111.4481	$111.45	$111.45	$111.40
7 purchase totals =	$719.58		$799.4460	$799.44	$799.45	$799.30