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	$248.97	12.511%	$280.1186	$280.12	$280.10	$280.10
Purchase #2	$241.80	11.116%	$268.6785	$268.68	$268.70	$268.70
Purchase #3	$17.80	5.328%	$18.7484	$18.75	$18.75	$18.70
Purchase #4	$58.36	9.530%	$63.9217	$63.92	$63.90	$63.90
Purchase #5	$9.68	12.352%	$10.8757	$10.88	$10.90	$10.90
Purchase #6	$235.96	3.361%	$243.8906	$243.89	$243.90	$243.90
Purchase #7	$187.39	4.794%	$196.3735	$196.37	$196.35	$196.40
7 purchase totals =	$999.96		$1,082.6070	$1,082.61	$1,082.60	$1,082.60