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	$142.75	9.734%	$156.6453	$156.65	$156.65	$156.60
Purchase #2	$247.64	6.226%	$263.0581	$263.06	$263.05	$263.10
Purchase #3	$51.53	10.346%	$56.8613	$56.86	$56.85	$56.90
Purchase #4	$42.34	13.693%	$48.1376	$48.14	$48.15	$48.10
Purchase #5	$121.28	8.759%	$131.9029	$131.90	$131.90	$131.90
Purchase #6	$38.97	6.562%	$41.5272	$41.53	$41.55	$41.50
Purchase #7	$109.71	12.776%	$123.7265	$123.73	$123.75	$123.70
7 purchase totals =	$754.22		$821.8589	$821.87	$821.90	$821.80