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	$235.54	13.814%	$268.0775	$268.08	$268.10	$268.10
Purchase #2	$197.89	6.674%	$211.0972	$211.10	$211.10	$211.10
Purchase #3	$248.94	12.495%	$280.0451	$280.05	$280.05	$280.00
Purchase #4	$58.32	12.216%	$65.4444	$65.44	$65.45	$65.40
Purchase #5	$151.41	3.191%	$156.2415	$156.24	$156.25	$156.20
Purchase #6	$150.83	11.272%	$167.8316	$167.83	$167.85	$167.80
Purchase #7	$92.91	8.543%	$100.8473	$100.85	$100.85	$100.80
7 purchase totals =	$1,135.84		$1,249.5846	$1,249.59	$1,249.65	$1,249.40