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	$96.73	12.170%	$108.502	$108.50	$108.50	$108.50
Purchase #2	$56.73	9.794%	$62.2861	$62.29	$62.30	$62.30
Purchase #3	$164.98	12.240%	$185.1736	$185.17	$185.15	$185.20
Purchase #4	$47.47	7.751%	$51.1494	$51.15	$51.15	$51.10
Purchase #5	$225.78	7.238%	$242.122	$242.12	$242.10	$242.10
Purchase #6	$150.73	3.494%	$155.9965	$156.00	$156.00	$156.00
Purchase #7	$228.56	11.165%	$254.0787	$254.08	$254.10	$254.10
7 purchase totals =	$970.98		$1,059.3083	$1,059.31	$1,059.30	$1,059.30