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	$140.37	13.690%	$159.5867	$159.59	$159.60	$159.60
Purchase #2	$27.30	3.785%	$28.3333	$28.33	$28.35	$28.30
Purchase #3	$132.92	6.858%	$142.0357	$142.04	$142.05	$142.00
Purchase #4	$109.67	12.667%	$123.5619	$123.56	$123.55	$123.60
Purchase #5	$37.74	11.117%	$41.9356	$41.94	$41.95	$41.90
Purchase #6	$44.72	10.783%	$49.5422	$49.54	$49.55	$49.50
Purchase #7	$236.53	12.359%	$265.7627	$265.76	$265.75	$265.80
7 purchase totals =	$729.25		$810.7581	$810.76	$810.80	$810.70