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	$202.67	9.309%	$221.5366	$221.54	$221.55	$221.50
Purchase #2	$195.52	13.750%	$222.404	$222.40	$222.40	$222.40
Purchase #3	$173.27	11.110%	$192.5203	$192.52	$192.50	$192.50
Purchase #4	$155.60	10.603%	$172.0983	$172.10	$172.10	$172.10
Purchase #5	$67.70	7.645%	$72.8757	$72.88	$72.90	$72.90
Purchase #6	$27.82	9.171%	$30.3714	$30.37	$30.35	$30.40
Purchase #7	$175.64	8.754%	$191.0155	$191.02	$191.00	$191.00
7 purchase totals =	$998.22		$1,102.8218	$1,102.83	$1,102.80	$1,102.80