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	$53.31	12.142%	$59.7829	$59.78	$59.80	$59.80
Purchase #2	$219.50	3.758%	$227.7488	$227.75	$227.75	$227.70
Purchase #3	$120.43	9.105%	$131.3952	$131.40	$131.40	$131.40
Purchase #4	$6.57	12.689%	$7.4037	$7.40	$7.40	$7.40
Purchase #5	$7.74	8.660%	$8.4103	$8.41	$8.40	$8.40
Purchase #6	$78.40	4.113%	$81.6246	$81.62	$81.60	$81.60
Purchase #7	$149.43	7.423%	$160.5222	$160.52	$160.50	$160.50
7 purchase totals =	$635.38		$676.8877	$676.88	$676.85	$676.80