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	$27.66	10.721%	$30.6254	$30.63	$30.65	$30.60
Purchase #2	$239.90	7.300%	$257.4127	$257.41	$257.40	$257.40
Purchase #3	$91.26	13.562%	$103.6367	$103.64	$103.65	$103.60
Purchase #4	$31.38	9.156%	$34.2532	$34.25	$34.25	$34.30
Purchase #5	$48.46	11.202%	$53.8885	$53.89	$53.90	$53.90
Purchase #6	$61.52	5.550%	$64.9344	$64.93	$64.95	$64.90
Purchase #7	$78.93	13.296%	$89.4245	$89.42	$89.40	$89.40
7 purchase totals =	$579.11		$634.1754	$634.17	$634.20	$634.10