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	$243.79	8.651%	$264.8803	$264.88	$264.90	$264.90
Purchase #2	$61.94	7.246%	$66.4282	$66.43	$66.45	$66.40
Purchase #3	$127.51	13.257%	$144.414	$144.41	$144.40	$144.40
Purchase #4	$33.30	11.477%	$37.1218	$37.12	$37.10	$37.10
Purchase #5	$36.42	6.303%	$38.7156	$38.72	$38.70	$38.70
Purchase #6	$246.79	10.809%	$273.4655	$273.47	$273.45	$273.50
Purchase #7	$28.68	11.710%	$32.0384	$32.04	$32.05	$32.00
7 purchase totals =	$778.43		$857.0638	$857.07	$857.05	$857.00