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	$241.34	12.496%	$271.4978	$271.50	$271.50	$271.50
Purchase #2	$180.33	5.124%	$189.5701	$189.57	$189.55	$189.60
Purchase #3	$168.96	3.291%	$174.5205	$174.52	$174.50	$174.50
Purchase #4	$50.54	7.152%	$54.1546	$54.15	$54.15	$54.20
Purchase #5	$91.58	9.774%	$100.531	$100.53	$100.55	$100.50
Purchase #6	$6.52	5.168%	$6.857	$6.86	$6.85	$6.90
Purchase #7	$185.99	11.862%	$208.0521	$208.05	$208.05	$208.10
7 purchase totals =	$925.26		$1,005.1831	$1,005.18	$1,005.15	$1,005.30