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	$12.60	4.740%	$13.1972	$13.20	$13.20	$13.20
Purchase #2	$52.48	4.266%	$54.7188	$54.72	$54.70	$54.70
Purchase #3	$128.98	12.453%	$145.0419	$145.04	$145.05	$145.00
Purchase #4	$11.54	6.181%	$12.2533	$12.25	$12.25	$12.30
Purchase #5	$132.60	9.398%	$145.0617	$145.06	$145.05	$145.10
Purchase #6	$165.33	12.824%	$186.5319	$186.53	$186.55	$186.50
Purchase #7	$75.52	13.766%	$85.9161	$85.92	$85.90	$85.90
7 purchase totals =	$579.05		$642.7209	$642.72	$642.70	$642.70