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	$136.83	4.178%	$142.5468	$142.55	$142.55	$142.50
Purchase #2	$104.42	4.839%	$109.4729	$109.47	$109.45	$109.50
Purchase #3	$242.99	11.398%	$270.686	$270.69	$270.70	$270.70
Purchase #4	$216.82	13.412%	$245.8999	$245.90	$245.90	$245.90
Purchase #5	$34.47	9.499%	$37.7443	$37.74	$37.75	$37.70
Purchase #6	$108.36	5.737%	$114.5766	$114.58	$114.60	$114.60
Purchase #7	$56.61	7.663%	$60.948	$60.95	$60.95	$60.90
7 purchase totals =	$900.50		$981.8745	$981.88	$981.90	$981.80