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	$82.78	6.442%	$88.1127	$88.11	$88.10	$88.10
Purchase #2	$214.49	12.645%	$241.6123	$241.61	$241.60	$241.60
Purchase #3	$132.29	13.343%	$149.9415	$149.94	$149.95	$149.90
Purchase #4	$162.31	4.266%	$169.2341	$169.23	$169.25	$169.20
Purchase #5	$12.80	4.232%	$13.3417	$13.34	$13.35	$13.30
Purchase #6	$50.86	7.324%	$54.585	$54.59	$54.60	$54.60
Purchase #7	$68.63	5.597%	$72.4712	$72.47	$72.45	$72.50
7 purchase totals =	$724.16		$789.2985	$789.29	$789.30	$789.20