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	$136.57	4.772%	$143.0871	$143.09	$143.10	$143.10
Purchase #2	$119.67	11.803%	$133.7947	$133.79	$133.80	$133.80
Purchase #3	$230.61	10.614%	$255.0869	$255.09	$255.10	$255.10
Purchase #4	$132.43	13.533%	$150.3518	$150.35	$150.35	$150.40
Purchase #5	$43.98	8.712%	$47.8115	$47.81	$47.80	$47.80
Purchase #6	$209.42	12.678%	$235.9703	$235.97	$235.95	$236.00
Purchase #7	$177.86	10.431%	$196.4126	$196.41	$196.40	$196.40
7 purchase totals =	$1,050.54		$1,162.5149	$1,162.51	$1,162.50	$1,162.60