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	$136.45	6.284%	$145.0245	$145.02	$145.00	$145.00
Purchase #2	$133.43	12.863%	$150.5931	$150.59	$150.60	$150.60
Purchase #3	$56.87	4.295%	$59.3126	$59.31	$59.30	$59.30
Purchase #4	$12.52	3.706%	$12.984	$12.98	$13.00	$13.00
Purchase #5	$129.48	9.157%	$141.3365	$141.34	$141.35	$141.30
Purchase #6	$136.30	5.851%	$144.2749	$144.27	$144.25	$144.30
Purchase #7	$194.93	9.222%	$212.9064	$212.91	$212.90	$212.90
7 purchase totals =	$799.98		$866.4320	$866.42	$866.40	$866.40