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	$148.58	10.799%	$164.6252	$164.63	$164.65	$164.60
Purchase #2	$63.46	7.325%	$68.1084	$68.11	$68.10	$68.10
Purchase #3	$33.99	10.320%	$37.4978	$37.50	$37.50	$37.50
Purchase #4	$111.58	9.299%	$121.9558	$121.96	$121.95	$122.00
Purchase #5	$6.70	12.187%	$7.5165	$7.52	$7.50	$7.50
Purchase #6	$81.77	4.631%	$85.5568	$85.56	$85.55	$85.60
Purchase #7	$93.77	12.456%	$105.45	$105.45	$105.45	$105.50
7 purchase totals =	$539.85		$590.7105	$590.73	$590.70	$590.80