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	$28.87	8.147%	$31.222	$31.22	$31.20	$31.20
Purchase #2	$37.43	13.427%	$42.4557	$42.46	$42.45	$42.50
Purchase #3	$24.78	11.733%	$27.6874	$27.69	$27.70	$27.70
Purchase #4	$143.93	7.811%	$155.1724	$155.17	$155.15	$155.20
Purchase #5	$47.88	7.431%	$51.438	$51.44	$51.45	$51.40
Purchase #6	$180.43	4.689%	$188.8904	$188.89	$188.90	$188.90
Purchase #7	$239.85	7.301%	$257.3614	$257.36	$257.35	$257.40
7 purchase totals =	$703.17		$754.2273	$754.23	$754.20	$754.30