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	$80.62	9.822%	$88.5385	$88.54	$88.55	$88.50
Purchase #2	$78.79	8.353%	$85.3713	$85.37	$85.35	$85.40
Purchase #3	$39.47	11.500%	$44.0091	$44.01	$44.00	$44.00
Purchase #4	$20.56	3.302%	$21.2389	$21.24	$21.25	$21.20
Purchase #5	$201.77	8.779%	$219.4834	$219.48	$219.50	$219.50
Purchase #6	$152.92	5.665%	$161.5829	$161.58	$161.60	$161.60
Purchase #7	$18.90	11.865%	$21.1425	$21.14	$21.15	$21.10
7 purchase totals =	$593.03		$641.3666	$641.36	$641.40	$641.30