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	$78.54	5.427%	$82.8024	$82.80	$82.80	$82.80
Purchase #2	$226.72	12.402%	$254.8378	$254.84	$254.85	$254.80
Purchase #3	$193.33	3.580%	$200.2512	$200.25	$200.25	$200.30
Purchase #4	$129.99	10.617%	$143.791	$143.79	$143.80	$143.80
Purchase #5	$195.51	12.660%	$220.2616	$220.26	$220.25	$220.30
Purchase #6	$81.85	8.855%	$89.0978	$89.10	$89.10	$89.10
Purchase #7	$130.33	7.410%	$139.9875	$139.99	$140.00	$140.00
7 purchase totals =	$1,036.27		$1,131.0293	$1,131.03	$1,131.05	$1,131.10