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	$232.29	11.679%	$259.4191	$259.42	$259.40	$259.40
Purchase #2	$178.48	6.748%	$190.5238	$190.52	$190.50	$190.50
Purchase #3	$67.70	7.542%	$72.8059	$72.81	$72.80	$72.80
Purchase #4	$206.57	11.801%	$230.9473	$230.95	$230.95	$230.90
Purchase #5	$135.43	11.488%	$150.9882	$150.99	$151.00	$151.00
Purchase #6	$40.78	11.197%	$45.3461	$45.35	$45.35	$45.30
Purchase #7	$154.28	5.385%	$162.588	$162.59	$162.60	$162.60
7 purchase totals =	$1,015.53		$1,112.6184	$1,112.63	$1,112.60	$1,112.50