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	$156.35	6.333%	$166.2516	$166.25	$166.25	$166.30
Purchase #2	$15.59	12.661%	$17.5638	$17.56	$17.55	$17.60
Purchase #3	$33.27	13.404%	$37.7295	$37.73	$37.75	$37.70
Purchase #4	$172.34	10.807%	$190.9648	$190.96	$190.95	$191.00
Purchase #5	$37.50	4.665%	$39.2494	$39.25	$39.25	$39.20
Purchase #6	$20.82	6.637%	$22.2018	$22.20	$22.20	$22.20
Purchase #7	$162.86	6.461%	$173.3824	$173.38	$173.40	$173.40
7 purchase totals =	$598.73		$647.3433	$647.33	$647.35	$647.40