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	$139.97	12.232%	$157.0911	$157.09	$157.10	$157.10
Purchase #2	$123.29	3.741%	$127.9023	$127.90	$127.90	$127.90
Purchase #3	$238.28	12.553%	$268.1913	$268.19	$268.20	$268.20
Purchase #4	$105.76	13.774%	$120.3274	$120.33	$120.35	$120.30
Purchase #5	$176.97	4.850%	$185.553	$185.55	$185.55	$185.60
Purchase #6	$85.31	7.603%	$91.7961	$91.80	$91.80	$91.80
Purchase #7	$241.59	8.642%	$262.4682	$262.47	$262.45	$262.50
7 purchase totals =	$1,111.17		$1,213.3294	$1,213.33	$1,213.35	$1,213.40