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	$71.94	6.246%	$76.4334	$76.43	$76.45	$76.40
Purchase #2	$232.96	3.356%	$240.7781	$240.78	$240.80	$240.80
Purchase #3	$35.80	7.440%	$38.4635	$38.46	$38.45	$38.50
Purchase #4	$200.82	10.292%	$221.4884	$221.49	$221.50	$221.50
Purchase #5	$59.75	11.274%	$66.4862	$66.49	$66.50	$66.50
Purchase #6	$132.32	9.606%	$145.0307	$145.03	$145.05	$145.00
Purchase #7	$159.80	13.566%	$181.4785	$181.48	$181.50	$181.50
7 purchase totals =	$893.39		$970.1588	$970.16	$970.25	$970.20