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	$32.68	3.416%	$33.7963	$33.80	$33.80	$33.80
Purchase #2	$92.69	8.835%	$100.8792	$100.88	$100.90	$100.90
Purchase #3	$212.84	13.248%	$241.037	$241.04	$241.05	$241.00
Purchase #4	$104.84	6.601%	$111.7605	$111.76	$111.75	$111.80
Purchase #5	$24.63	4.808%	$25.8142	$25.81	$25.80	$25.80
Purchase #6	$31.90	9.442%	$34.912	$34.91	$34.90	$34.90
Purchase #7	$145.53	4.567%	$152.1764	$152.18	$152.20	$152.20
7 purchase totals =	$645.11		$700.3756	$700.38	$700.40	$700.40