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	$81.72	10.725%	$90.4845	$90.48	$90.50	$90.50
Purchase #2	$175.64	6.361%	$186.8125	$186.81	$186.80	$186.80
Purchase #3	$90.89	3.386%	$93.9675	$93.97	$93.95	$94.00
Purchase #4	$71.51	9.152%	$78.0546	$78.05	$78.05	$78.10
Purchase #5	$103.56	7.563%	$111.3922	$111.39	$111.40	$111.40
Purchase #6	$236.32	4.218%	$246.288	$246.29	$246.30	$246.30
Purchase #7	$25.40	13.845%	$28.9166	$28.92	$28.90	$28.90
7 purchase totals =	$785.04		$835.9159	$835.91	$835.90	$836.00