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	$57.91	11.711%	$64.6918	$64.69	$64.70	$64.70
Purchase #2	$158.55	6.475%	$168.8161	$168.82	$168.80	$168.80
Purchase #3	$125.91	12.702%	$141.9031	$141.90	$141.90	$141.90
Purchase #4	$158.42	12.205%	$177.7552	$177.76	$177.75	$177.80
Purchase #5	$111.93	6.483%	$119.1864	$119.19	$119.20	$119.20
Purchase #6	$11.82	13.127%	$13.3716	$13.37	$13.35	$13.40
Purchase #7	$40.88	4.387%	$42.6734	$42.67	$42.65	$42.70
7 purchase totals =	$665.42		$728.3976	$728.40	$728.35	$728.50