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	$38.52	9.377%	$42.132	$42.13	$42.15	$42.10
Purchase #2	$38.76	13.156%	$43.8593	$43.86	$43.85	$43.90
Purchase #3	$11.54	13.285%	$13.0731	$13.07	$13.05	$13.10
Purchase #4	$105.70	3.733%	$109.6458	$109.65	$109.65	$109.60
Purchase #5	$41.39	7.680%	$44.5688	$44.57	$44.55	$44.60
Purchase #6	$240.72	13.404%	$272.9861	$272.99	$273.00	$273.00
Purchase #7	$152.50	12.562%	$171.6571	$171.66	$171.65	$171.70
7 purchase totals =	$629.13		$697.9222	$697.93	$697.90	$698.00