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	$9.88	6.567%	$10.5288	$10.53	$10.55	$10.50
Purchase #2	$55.53	7.619%	$59.7608	$59.76	$59.75	$59.80
Purchase #3	$78.28	9.264%	$85.5319	$85.53	$85.55	$85.50
Purchase #4	$113.93	6.499%	$121.3343	$121.33	$121.35	$121.30
Purchase #5	$123.90	8.516%	$134.4513	$134.45	$134.45	$134.50
Purchase #6	$67.31	13.110%	$76.1343	$76.13	$76.15	$76.10
Purchase #7	$74.26	12.568%	$83.593	$83.59	$83.60	$83.60
7 purchase totals =	$523.09		$571.3344	$571.32	$571.40	$571.30