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	$245.25	7.739%	$264.2299	$264.23	$264.25	$264.20
Purchase #2	$184.74	6.533%	$196.8091	$196.81	$196.80	$196.80
Purchase #3	$62.46	10.177%	$68.8166	$68.82	$68.80	$68.80
Purchase #4	$166.90	9.389%	$182.5702	$182.57	$182.55	$182.60
Purchase #5	$49.51	7.789%	$53.3663	$53.37	$53.35	$53.40
Purchase #6	$24.28	5.623%	$25.6453	$25.65	$25.65	$25.60
Purchase #7	$38.31	11.795%	$42.8287	$42.83	$42.85	$42.80
7 purchase totals =	$771.45		$834.2661	$834.28	$834.25	$834.20