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	$27.84	12.851%	$31.4177	$31.42	$31.40	$31.40
Purchase #2	$236.97	3.676%	$245.681	$245.68	$245.70	$245.70
Purchase #3	$38.37	8.240%	$41.5317	$41.53	$41.55	$41.50
Purchase #4	$104.50	12.658%	$117.7276	$117.73	$117.75	$117.70
Purchase #5	$42.64	13.531%	$48.4096	$48.41	$48.40	$48.40
Purchase #6	$243.80	4.505%	$254.7832	$254.78	$254.80	$254.80
Purchase #7	$225.47	13.218%	$255.2726	$255.27	$255.25	$255.30
7 purchase totals =	$919.59		$994.8234	$994.82	$994.85	$994.80