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	$94.29	10.216%	$103.9227	$103.92	$103.90	$103.90
Purchase #2	$192.85	7.769%	$207.8325	$207.83	$207.85	$207.80
Purchase #3	$30.95	5.637%	$32.6947	$32.69	$32.70	$32.70
Purchase #4	$83.90	7.337%	$90.0557	$90.06	$90.05	$90.10
Purchase #5	$126.88	13.506%	$144.0164	$144.02	$144.00	$144.00
Purchase #6	$237.71	6.783%	$253.8339	$253.83	$253.85	$253.80
Purchase #7	$11.85	12.309%	$13.3086	$13.31	$13.30	$13.30
7 purchase totals =	$778.43		$845.6645	$845.66	$845.65	$845.60