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	$33.44	11.831%	$37.3963	$37.40	$37.40	$37.40
Purchase #2	$104.62	12.299%	$117.4872	$117.49	$117.50	$117.50
Purchase #3	$85.77	4.456%	$89.5919	$89.59	$89.60	$89.60
Purchase #4	$122.99	6.364%	$130.8171	$130.82	$130.80	$130.80
Purchase #5	$234.26	10.833%	$259.6374	$259.64	$259.65	$259.60
Purchase #6	$134.38	4.274%	$140.1234	$140.12	$140.10	$140.10
Purchase #7	$208.37	7.711%	$224.4374	$224.44	$224.45	$224.40
7 purchase totals =	$923.83		$999.4907	$999.50	$999.50	$999.40