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	$27.89	12.440%	$31.3595	$31.36	$31.35	$31.40
Purchase #2	$90.50	4.407%	$94.4883	$94.49	$94.50	$94.50
Purchase #3	$73.49	6.809%	$78.4939	$78.49	$78.50	$78.50
Purchase #4	$39.29	12.676%	$44.2704	$44.27	$44.25	$44.30
Purchase #5	$48.85	5.508%	$51.5407	$51.54	$51.55	$51.50
Purchase #6	$215.73	8.383%	$233.8146	$233.81	$233.80	$233.80
Purchase #7	$188.46	7.527%	$202.6454	$202.65	$202.65	$202.60
7 purchase totals =	$684.21		$736.6128	$736.61	$736.60	$736.60