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	$57.29	3.771%	$59.4504	$59.45	$59.45	$59.50
Purchase #2	$148.75	13.429%	$168.7256	$168.73	$168.75	$168.70
Purchase #3	$124.60	3.706%	$129.2177	$129.22	$129.20	$129.20
Purchase #4	$164.40	9.241%	$179.5922	$179.59	$179.60	$179.60
Purchase #5	$80.32	4.535%	$83.9625	$83.96	$83.95	$84.00
Purchase #6	$48.58	8.709%	$52.8108	$52.81	$52.80	$52.80
Purchase #7	$231.49	9.359%	$253.1551	$253.16	$253.15	$253.20
7 purchase totals =	$855.43		$926.9143	$926.92	$926.90	$927.00