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	$121.74	6.623%	$129.8028	$129.80	$129.80	$129.80
Purchase #2	$68.66	5.424%	$72.3841	$72.38	$72.40	$72.40
Purchase #3	$29.52	9.509%	$32.3271	$32.33	$32.35	$32.30
Purchase #4	$244.41	12.195%	$274.2158	$274.22	$274.20	$274.20
Purchase #5	$183.96	3.484%	$190.3692	$190.37	$190.35	$190.40
Purchase #6	$108.87	13.706%	$123.7917	$123.79	$123.80	$123.80
Purchase #7	$216.73	10.804%	$240.1455	$240.15	$240.15	$240.10
7 purchase totals =	$973.89		$1,063.0362	$1,063.04	$1,063.05	$1,063.00