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	$19.92	9.791%	$21.8704	$21.87	$21.85	$21.90
Purchase #2	$168.96	3.635%	$175.1017	$175.10	$175.10	$175.10
Purchase #3	$130.60	8.765%	$142.0471	$142.05	$142.05	$142.00
Purchase #4	$176.37	13.584%	$200.3281	$200.33	$200.35	$200.30
Purchase #5	$91.48	10.295%	$100.8979	$100.90	$100.90	$100.90
Purchase #6	$6.43	8.248%	$6.9603	$6.96	$6.95	$7.00
Purchase #7	$231.42	3.226%	$238.8856	$238.89	$238.90	$238.90
7 purchase totals =	$825.18		$886.0911	$886.10	$886.10	$886.10