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	$28.77	13.689%	$32.7083	$32.71	$32.70	$32.70
Purchase #2	$38.90	6.610%	$41.4713	$41.47	$41.45	$41.50
Purchase #3	$188.65	3.250%	$194.7811	$194.78	$194.80	$194.80
Purchase #4	$244.91	4.634%	$256.2591	$256.26	$256.25	$256.30
Purchase #5	$52.74	12.139%	$59.1421	$59.14	$59.15	$59.10
Purchase #6	$5.61	13.295%	$6.3558	$6.36	$6.35	$6.40
Purchase #7	$87.69	9.426%	$95.9557	$95.96	$95.95	$96.00
7 purchase totals =	$647.27		$686.6734	$686.68	$686.65	$686.80