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	$78.82	13.375%	$89.3622	$89.36	$89.35	$89.40
Purchase #2	$140.41	7.305%	$150.667	$150.67	$150.65	$150.70
Purchase #3	$58.76	7.516%	$63.1764	$63.18	$63.20	$63.20
Purchase #4	$235.80	8.176%	$255.079	$255.08	$255.10	$255.10
Purchase #5	$45.28	3.473%	$46.8526	$46.85	$46.85	$46.90
Purchase #6	$166.46	6.720%	$177.6461	$177.65	$177.65	$177.60
Purchase #7	$59.31	10.417%	$65.4883	$65.49	$65.50	$65.50
7 purchase totals =	$784.84		$848.2716	$848.28	$848.30	$848.40