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	$34.27	13.314%	$38.8327	$38.83	$38.85	$38.80
Purchase #2	$31.69	13.206%	$35.875	$35.88	$35.90	$35.90
Purchase #3	$165.64	9.558%	$181.4719	$181.47	$181.45	$181.50
Purchase #4	$203.76	8.844%	$221.7805	$221.78	$221.80	$221.80
Purchase #5	$36.51	13.261%	$41.3516	$41.35	$41.35	$41.40
Purchase #6	$72.87	13.190%	$82.4816	$82.48	$82.50	$82.50
Purchase #7	$103.95	13.790%	$118.2847	$118.28	$118.30	$118.30
7 purchase totals =	$648.69		$720.0780	$720.07	$720.15	$720.20