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	$32.54	5.844%	$34.4416	$34.44	$34.45	$34.40
Purchase #2	$97.48	3.228%	$100.6267	$100.63	$100.65	$100.60
Purchase #3	$61.42	10.108%	$67.6283	$67.63	$67.65	$67.60
Purchase #4	$131.66	11.553%	$146.8707	$146.87	$146.85	$146.90
Purchase #5	$171.40	3.645%	$177.6475	$177.65	$177.65	$177.60
Purchase #6	$190.71	5.243%	$200.7089	$200.71	$200.70	$200.70
Purchase #7	$72.49	13.516%	$82.2877	$82.29	$82.30	$82.30
7 purchase totals =	$757.70		$810.2114	$810.22	$810.25	$810.10