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	$37.34	13.719%	$42.4627	$42.46	$42.45	$42.50
Purchase #2	$161.28	10.290%	$177.8757	$177.88	$177.90	$177.90
Purchase #3	$60.63	3.227%	$62.5865	$62.59	$62.60	$62.60
Purchase #4	$178.63	10.233%	$196.9092	$196.91	$196.90	$196.90
Purchase #5	$128.37	3.264%	$132.56	$132.56	$132.55	$132.60
Purchase #6	$211.96	10.717%	$234.6758	$234.68	$234.70	$234.70
Purchase #7	$7.50	12.819%	$8.4614	$8.46	$8.45	$8.50
7 purchase totals =	$785.71		$855.5313	$855.54	$855.55	$855.70