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	$100.38	11.558%	$111.9819	$111.98	$112.00	$112.00
Purchase #2	$122.76	5.623%	$129.6628	$129.66	$129.65	$129.70
Purchase #3	$25.37	9.474%	$27.7736	$27.77	$27.75	$27.80
Purchase #4	$151.53	3.273%	$156.4896	$156.49	$156.50	$156.50
Purchase #5	$138.95	8.132%	$150.2494	$150.25	$150.25	$150.20
Purchase #6	$79.39	12.654%	$89.436	$89.44	$89.45	$89.40
Purchase #7	$210.67	5.384%	$222.0125	$222.01	$222.00	$222.00
7 purchase totals =	$829.05		$887.6058	$887.60	$887.60	$887.60