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	$38.87	9.288%	$42.4802	$42.48	$42.50	$42.50
Purchase #2	$148.82	12.376%	$167.238	$167.24	$167.25	$167.20
Purchase #3	$130.79	9.206%	$142.8305	$142.83	$142.85	$142.80
Purchase #4	$145.62	4.262%	$151.8263	$151.83	$151.85	$151.80
Purchase #5	$31.69	6.398%	$33.7175	$33.72	$33.70	$33.70
Purchase #6	$245.31	5.401%	$258.5592	$258.56	$258.55	$258.60
Purchase #7	$19.63	6.387%	$20.8838	$20.88	$20.90	$20.90
7 purchase totals =	$760.73		$817.5355	$817.54	$817.60	$817.50