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	$240.43	4.594%	$251.4754	$251.48	$251.50	$251.50
Purchase #2	$108.75	3.850%	$112.9369	$112.94	$112.95	$112.90
Purchase #3	$45.92	8.508%	$49.8269	$49.83	$49.85	$49.80
Purchase #4	$106.40	12.620%	$119.8277	$119.83	$119.85	$119.80
Purchase #5	$59.76	3.566%	$61.891	$61.89	$61.90	$61.90
Purchase #6	$105.40	3.813%	$109.4189	$109.42	$109.40	$109.40
Purchase #7	$128.90	11.556%	$143.7957	$143.80	$143.80	$143.80
7 purchase totals =	$795.56		$849.1725	$849.19	$849.25	$849.10