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	$127.33	11.789%	$142.3409	$142.34	$142.35	$142.30
Purchase #2	$113.72	5.109%	$119.53	$119.53	$119.55	$119.50
Purchase #3	$25.25	7.686%	$27.1907	$27.19	$27.20	$27.20
Purchase #4	$116.31	6.397%	$123.7504	$123.75	$123.75	$123.80
Purchase #5	$92.68	8.158%	$100.2408	$100.24	$100.25	$100.20
Purchase #6	$48.28	4.626%	$50.5134	$50.51	$50.50	$50.50
Purchase #7	$234.34	8.740%	$254.8213	$254.82	$254.80	$254.80
7 purchase totals =	$757.91		$818.3875	$818.38	$818.40	$818.30