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	$83.77	8.420%	$90.8234	$90.82	$90.80	$90.80
Purchase #2	$127.66	11.718%	$142.6192	$142.62	$142.60	$142.60
Purchase #3	$36.51	8.478%	$39.6053	$39.61	$39.60	$39.60
Purchase #4	$59.29	13.847%	$67.4999	$67.50	$67.50	$67.50
Purchase #5	$115.90	6.456%	$123.3825	$123.38	$123.40	$123.40
Purchase #6	$232.56	10.442%	$256.8439	$256.84	$256.85	$256.80
Purchase #7	$216.97	12.376%	$243.8222	$243.82	$243.80	$243.80
7 purchase totals =	$872.66		$964.5964	$964.59	$964.55	$964.50