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	$109.86	8.144%	$118.807	$118.81	$118.80	$118.80
Purchase #2	$181.56	13.201%	$205.5277	$205.53	$205.55	$205.50
Purchase #3	$37.34	7.522%	$40.1487	$40.15	$40.15	$40.10
Purchase #4	$48.53	13.107%	$54.8908	$54.89	$54.90	$54.90
Purchase #5	$61.47	13.551%	$69.7998	$69.80	$69.80	$69.80
Purchase #6	$79.59	4.741%	$83.3634	$83.36	$83.35	$83.40
Purchase #7	$134.73	13.534%	$152.9644	$152.96	$152.95	$153.00
7 purchase totals =	$653.08		$725.5018	$725.50	$725.50	$725.50