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	$229.67	13.124%	$259.8119	$259.81	$259.80	$259.80
Purchase #2	$108.73	10.133%	$119.7476	$119.75	$119.75	$119.70
Purchase #3	$62.79	5.566%	$66.2849	$66.28	$66.30	$66.30
Purchase #4	$21.89	7.630%	$23.5602	$23.56	$23.55	$23.60
Purchase #5	$167.75	7.769%	$180.7825	$180.78	$180.80	$180.80
Purchase #6	$25.73	11.572%	$28.7075	$28.71	$28.70	$28.70
Purchase #7	$189.96	3.647%	$196.8878	$196.89	$196.90	$196.90
7 purchase totals =	$806.52		$875.7824	$875.78	$875.80	$875.80