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	$69.41	13.538%	$78.8067	$78.81	$78.80	$78.80
Purchase #2	$193.78	12.461%	$217.9269	$217.93	$217.95	$217.90
Purchase #3	$100.73	7.270%	$108.0531	$108.05	$108.05	$108.10
Purchase #4	$174.66	4.744%	$182.9459	$182.95	$182.95	$182.90
Purchase #5	$32.87	13.261%	$37.2289	$37.23	$37.25	$37.20
Purchase #6	$57.78	10.845%	$64.0462	$64.05	$64.05	$64.00
Purchase #7	$29.49	13.839%	$33.5711	$33.57	$33.55	$33.60
7 purchase totals =	$658.72		$722.5788	$722.59	$722.60	$722.50