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	$66.25	7.242%	$71.0478	$71.05	$71.05	$71.00
Purchase #2	$104.74	9.242%	$114.4201	$114.42	$114.40	$114.40
Purchase #3	$100.82	9.421%	$110.3183	$110.32	$110.30	$110.30
Purchase #4	$10.73	6.710%	$11.45	$11.45	$11.45	$11.50
Purchase #5	$72.93	7.687%	$78.5361	$78.54	$78.55	$78.50
Purchase #6	$174.44	5.509%	$184.0499	$184.05	$184.05	$184.00
Purchase #7	$25.98	7.500%	$27.9285	$27.93	$27.95	$27.90
7 purchase totals =	$555.89		$597.7507	$597.76	$597.75	$597.60