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	$52.41	7.284%	$56.2275	$56.23	$56.25	$56.20
Purchase #2	$131.88	12.243%	$148.0261	$148.03	$148.05	$148.00
Purchase #3	$48.78	8.853%	$53.0985	$53.10	$53.10	$53.10
Purchase #4	$64.45	13.179%	$72.9439	$72.94	$72.95	$72.90
Purchase #5	$186.40	5.191%	$196.076	$196.08	$196.10	$196.10
Purchase #6	$194.87	6.209%	$206.9695	$206.97	$206.95	$207.00
Purchase #7	$91.42	13.736%	$103.9775	$103.98	$104.00	$104.00
7 purchase totals =	$770.21		$837.3190	$837.33	$837.40	$837.30