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	$43.67	13.189%	$49.4296	$49.43	$49.45	$49.40
Purchase #2	$117.89	4.801%	$123.5499	$123.55	$123.55	$123.50
Purchase #3	$66.53	5.785%	$70.3788	$70.38	$70.40	$70.40
Purchase #4	$38.57	10.256%	$42.5257	$42.53	$42.55	$42.50
Purchase #5	$22.75	13.580%	$25.8395	$25.84	$25.85	$25.80
Purchase #6	$80.64	9.483%	$88.2871	$88.29	$88.30	$88.30
Purchase #7	$70.44	6.735%	$75.1841	$75.18	$75.20	$75.20
7 purchase totals =	$440.49		$475.1947	$475.20	$475.30	$475.10