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	$33.76	9.560%	$36.9875	$36.99	$37.00	$37.00
Purchase #2	$121.32	4.749%	$127.0815	$127.08	$127.10	$127.10
Purchase #3	$147.43	11.268%	$164.0424	$164.04	$164.05	$164.00
Purchase #4	$52.30	10.666%	$57.8783	$57.88	$57.90	$57.90
Purchase #5	$232.41	3.241%	$239.9424	$239.94	$239.95	$239.90
Purchase #6	$127.26	3.343%	$131.5143	$131.51	$131.50	$131.50
Purchase #7	$121.75	9.464%	$133.2724	$133.27	$133.25	$133.30
7 purchase totals =	$836.23		$890.7188	$890.71	$890.75	$890.70