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	$26.34	4.808%	$27.6064	$27.61	$27.60	$27.60
Purchase #2	$156.51	7.272%	$167.8914	$167.89	$167.90	$167.90
Purchase #3	$52.82	4.248%	$55.0638	$55.06	$55.05	$55.10
Purchase #4	$13.69	9.871%	$15.0413	$15.04	$15.05	$15.00
Purchase #5	$63.65	7.811%	$68.6217	$68.62	$68.60	$68.60
Purchase #6	$11.37	8.276%	$12.311	$12.31	$12.30	$12.30
Purchase #7	$126.66	12.131%	$142.0251	$142.03	$142.05	$142.00
7 purchase totals =	$451.04		$488.5607	$488.56	$488.55	$488.50