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	$78.76	13.301%	$89.2359	$89.24	$89.25	$89.20
Purchase #2	$43.54	10.780%	$48.2336	$48.23	$48.25	$48.20
Purchase #3	$201.92	6.787%	$215.6243	$215.62	$215.60	$215.60
Purchase #4	$28.73	4.199%	$29.9364	$29.94	$29.95	$29.90
Purchase #5	$85.95	4.426%	$89.7541	$89.75	$89.75	$89.80
Purchase #6	$48.93	9.345%	$53.5025	$53.50	$53.50	$53.50
Purchase #7	$124.68	12.172%	$139.856	$139.86	$139.85	$139.90
7 purchase totals =	$612.51		$666.1428	$666.14	$666.15	$666.10