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	$238.35	5.426%	$251.2829	$251.28	$251.30	$251.30
Purchase #2	$91.68	11.574%	$102.291	$102.29	$102.30	$102.30
Purchase #3	$177.34	10.632%	$196.1948	$196.19	$196.20	$196.20
Purchase #4	$179.72	11.507%	$200.4004	$200.40	$200.40	$200.40
Purchase #5	$113.49	9.258%	$123.9969	$124.00	$124.00	$124.00
Purchase #6	$165.92	7.801%	$178.8634	$178.86	$178.85	$178.90
Purchase #7	$108.40	9.829%	$119.0546	$119.05	$119.05	$119.10
7 purchase totals =	$1,074.90		$1,172.0840	$1,172.07	$1,172.10	$1,172.20