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	$26.60	12.357%	$29.887	$29.89	$29.90	$29.90
Purchase #2	$95.73	7.165%	$102.5891	$102.59	$102.60	$102.60
Purchase #3	$137.95	10.526%	$152.4706	$152.47	$152.45	$152.50
Purchase #4	$79.93	5.419%	$84.2614	$84.26	$84.25	$84.30
Purchase #5	$246.86	11.429%	$275.0736	$275.07	$275.05	$275.10
Purchase #6	$125.72	13.556%	$142.7626	$142.76	$142.75	$142.80
Purchase #7	$200.32	12.248%	$224.8552	$224.86	$224.85	$224.90
7 purchase totals =	$913.11		$1,011.8995	$1,011.90	$1,011.85	$1,012.10