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	$85.97	5.824%	$90.9769	$90.98	$91.00	$91.00
Purchase #2	$213.61	4.569%	$223.3698	$223.37	$223.35	$223.40
Purchase #3	$15.84	13.497%	$17.9779	$17.98	$18.00	$18.00
Purchase #4	$137.70	11.218%	$153.1472	$153.15	$153.15	$153.10
Purchase #5	$125.67	5.322%	$132.3582	$132.36	$132.35	$132.40
Purchase #6	$67.27	7.142%	$72.0744	$72.07	$72.05	$72.10
Purchase #7	$134.89	13.347%	$152.8938	$152.89	$152.90	$152.90
7 purchase totals =	$780.95		$842.7982	$842.80	$842.80	$842.90