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	$72.80	7.284%	$78.1028	$78.10	$78.10	$78.10
Purchase #2	$222.85	11.871%	$249.3045	$249.30	$249.30	$249.30
Purchase #3	$172.82	4.419%	$180.4569	$180.46	$180.45	$180.50
Purchase #4	$37.40	11.127%	$41.5615	$41.56	$41.55	$41.60
Purchase #5	$246.28	5.653%	$260.2022	$260.20	$260.20	$260.20
Purchase #6	$39.71	12.706%	$44.7556	$44.76	$44.75	$44.80
Purchase #7	$188.74	13.866%	$214.9107	$214.91	$214.90	$214.90
7 purchase totals =	$980.60		$1,069.2942	$1,069.29	$1,069.25	$1,069.40