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	$73.61	6.595%	$78.4646	$78.46	$78.45	$78.50
Purchase #2	$132.62	9.186%	$144.8025	$144.80	$144.80	$144.80
Purchase #3	$116.36	13.823%	$132.4444	$132.44	$132.45	$132.40
Purchase #4	$6.82	7.118%	$7.3054	$7.31	$7.30	$7.30
Purchase #5	$74.53	3.107%	$76.8456	$76.85	$76.85	$76.80
Purchase #6	$177.81	10.629%	$196.7094	$196.71	$196.70	$196.70
Purchase #7	$27.73	3.116%	$28.5941	$28.59	$28.60	$28.60
7 purchase totals =	$609.48		$665.1660	$665.16	$665.15	$665.10