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	$225.25	6.693%	$240.326	$240.33	$240.35	$240.30
Purchase #2	$156.59	10.411%	$172.8926	$172.89	$172.90	$172.90
Purchase #3	$134.99	10.333%	$148.9385	$148.94	$148.95	$148.90
Purchase #4	$128.37	9.374%	$140.4034	$140.40	$140.40	$140.40
Purchase #5	$87.82	7.729%	$94.6076	$94.61	$94.60	$94.60
Purchase #6	$60.72	6.646%	$64.7555	$64.76	$64.75	$64.80
Purchase #7	$126.83	11.849%	$141.8581	$141.86	$141.85	$141.90
7 purchase totals =	$920.57		$1,003.7817	$1,003.79	$1,003.80	$1,003.80