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	$164.81	11.803%	$184.2625	$184.26	$184.25	$184.30
Purchase #2	$101.25	5.464%	$106.7823	$106.78	$106.80	$106.80
Purchase #3	$232.43	5.110%	$244.3072	$244.31	$244.30	$244.30
Purchase #4	$180.67	5.477%	$190.5653	$190.57	$190.55	$190.60
Purchase #5	$75.85	3.779%	$78.7164	$78.72	$78.70	$78.70
Purchase #6	$26.80	6.363%	$28.5053	$28.51	$28.50	$28.50
Purchase #7	$63.74	5.817%	$67.4478	$67.45	$67.45	$67.40
7 purchase totals =	$845.55		$900.5868	$900.60	$900.55	$900.60