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	$20.42	7.211%	$21.8925	$21.89	$21.90	$21.90
Purchase #2	$182.81	4.215%	$190.5154	$190.52	$190.50	$190.50
Purchase #3	$238.44	11.386%	$265.5888	$265.59	$265.60	$265.60
Purchase #4	$139.33	13.771%	$158.5171	$158.52	$158.50	$158.50
Purchase #5	$218.72	13.111%	$247.3964	$247.40	$247.40	$247.40
Purchase #6	$167.33	4.817%	$175.3903	$175.39	$175.40	$175.40
Purchase #7	$205.87	5.111%	$216.392	$216.39	$216.40	$216.40
7 purchase totals =	$1,172.92		$1,275.6925	$1,275.70	$1,275.70	$1,275.70