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	$66.61	8.820%	$72.485	$72.49	$72.50	$72.50
Purchase #2	$71.64	4.737%	$75.0336	$75.03	$75.05	$75.00
Purchase #3	$45.39	3.854%	$47.1393	$47.14	$47.15	$47.10
Purchase #4	$148.70	6.403%	$158.2213	$158.22	$158.20	$158.20
Purchase #5	$109.81	12.323%	$123.3419	$123.34	$123.35	$123.30
Purchase #6	$121.87	8.217%	$131.8841	$131.88	$131.90	$131.90
Purchase #7	$238.49	4.747%	$249.8111	$249.81	$249.80	$249.80
7 purchase totals =	$802.51		$857.9163	$857.91	$857.95	$857.80