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	$75.89	3.663%	$78.6699	$78.67	$78.65	$78.70
Purchase #2	$98.77	11.132%	$109.7651	$109.77	$109.75	$109.80
Purchase #3	$68.50	4.394%	$71.5099	$71.51	$71.50	$71.50
Purchase #4	$127.26	3.240%	$131.3832	$131.38	$131.40	$131.40
Purchase #5	$127.63	5.206%	$134.2744	$134.27	$134.25	$134.30
Purchase #6	$84.78	6.348%	$90.1618	$90.16	$90.15	$90.20
Purchase #7	$126.33	12.463%	$142.0745	$142.07	$142.05	$142.10
7 purchase totals =	$709.16		$757.8388	$757.83	$757.75	$758.00