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	$231.86	10.470%	$256.1357	$256.14	$256.15	$256.10
Purchase #2	$89.51	6.164%	$95.0274	$95.03	$95.05	$95.00
Purchase #3	$134.56	3.461%	$139.2171	$139.22	$139.20	$139.20
Purchase #4	$63.39	12.752%	$71.4735	$71.47	$71.45	$71.50
Purchase #5	$64.51	7.874%	$69.5895	$69.59	$69.60	$69.60
Purchase #6	$236.93	13.310%	$268.4654	$268.47	$268.45	$268.50
Purchase #7	$83.26	8.612%	$90.4304	$90.43	$90.45	$90.40
7 purchase totals =	$904.02		$990.3390	$990.35	$990.35	$990.30