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	$47.32	10.591%	$52.3317	$52.33	$52.35	$52.30
Purchase #2	$39.98	7.218%	$42.8658	$42.87	$42.85	$42.90
Purchase #3	$56.50	9.295%	$61.7517	$61.75	$61.75	$61.80
Purchase #4	$142.33	6.400%	$151.4391	$151.44	$151.45	$151.40
Purchase #5	$216.25	7.761%	$233.0332	$233.03	$233.05	$233.00
Purchase #6	$81.52	12.780%	$91.9383	$91.94	$91.95	$91.90
Purchase #7	$23.50	3.605%	$24.3472	$24.35	$24.35	$24.30
7 purchase totals =	$607.40		$657.7070	$657.71	$657.75	$657.60