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	$96.78	6.663%	$103.2285	$103.23	$103.25	$103.20
Purchase #2	$143.50	7.201%	$153.8334	$153.83	$153.85	$153.80
Purchase #3	$102.39	7.861%	$110.4389	$110.44	$110.45	$110.40
Purchase #4	$54.34	9.345%	$59.4181	$59.42	$59.40	$59.40
Purchase #5	$172.51	7.366%	$185.2171	$185.22	$185.20	$185.20
Purchase #6	$234.39	13.557%	$266.1663	$266.17	$266.15	$266.20
Purchase #7	$114.64	5.529%	$120.9784	$120.98	$121.00	$121.00
7 purchase totals =	$918.55		$999.2807	$999.29	$999.30	$999.20