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	$93.80	10.640%	$103.7803	$103.78	$103.80	$103.80
Purchase #2	$52.68	9.174%	$57.5129	$57.51	$57.50	$57.50
Purchase #3	$97.34	3.336%	$100.5873	$100.59	$100.60	$100.60
Purchase #4	$128.73	4.580%	$134.6258	$134.63	$134.65	$134.60
Purchase #5	$5.63	5.638%	$5.9474	$5.95	$5.95	$5.90
Purchase #6	$58.57	6.365%	$62.298	$62.30	$62.30	$62.30
Purchase #7	$173.55	5.592%	$183.2549	$183.25	$183.25	$183.30
7 purchase totals =	$610.30		$648.0066	$648.01	$648.05	$648.00