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	$7.68	7.422%	$8.25	$8.25	$8.25	$8.30
Purchase #2	$51.55	12.253%	$57.8664	$57.87	$57.85	$57.90
Purchase #3	$35.55	6.311%	$37.7936	$37.79	$37.80	$37.80
Purchase #4	$68.84	13.649%	$78.236	$78.24	$78.25	$78.20
Purchase #5	$116.35	5.763%	$123.0553	$123.06	$123.05	$123.10
Purchase #6	$248.96	5.791%	$263.3773	$263.38	$263.40	$263.40
Purchase #7	$124.96	5.245%	$131.5142	$131.51	$131.50	$131.50
7 purchase totals =	$653.89		$700.0928	$700.10	$700.10	$700.20