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	$131.63	6.419%	$140.0793	$140.08	$140.10	$140.10
Purchase #2	$56.37	5.465%	$59.4506	$59.45	$59.45	$59.50
Purchase #3	$33.26	4.715%	$34.8282	$34.83	$34.85	$34.80
Purchase #4	$132.79	11.351%	$147.863	$147.86	$147.85	$147.90
Purchase #5	$171.75	12.871%	$193.8559	$193.86	$193.85	$193.90
Purchase #6	$204.75	10.316%	$225.872	$225.87	$225.85	$225.90
Purchase #7	$17.75	4.593%	$18.5653	$18.57	$18.55	$18.60
7 purchase totals =	$748.30		$820.5143	$820.52	$820.50	$820.70