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	$227.99	9.174%	$248.9058	$248.91	$248.90	$248.90
Purchase #2	$72.40	4.741%	$75.8325	$75.83	$75.85	$75.80
Purchase #3	$174.46	12.463%	$196.2029	$196.20	$196.20	$196.20
Purchase #4	$101.46	10.349%	$111.9601	$111.96	$111.95	$112.00
Purchase #5	$100.71	8.539%	$109.3096	$109.31	$109.30	$109.30
Purchase #6	$30.43	6.838%	$32.5108	$32.51	$32.50	$32.50
Purchase #7	$95.91	10.413%	$105.8971	$105.90	$105.90	$105.90
7 purchase totals =	$803.36		$880.6188	$880.62	$880.60	$880.60