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	$157.54	9.683%	$172.7946	$172.79	$172.80	$172.80
Purchase #2	$110.96	11.660%	$123.8979	$123.90	$123.90	$123.90
Purchase #3	$143.93	5.498%	$151.8433	$151.84	$151.85	$151.80
Purchase #4	$16.47	8.566%	$17.8808	$17.88	$17.90	$17.90
Purchase #5	$62.69	9.415%	$68.5923	$68.59	$68.60	$68.60
Purchase #6	$30.30	4.656%	$31.7108	$31.71	$31.70	$31.70
Purchase #7	$31.87	12.228%	$35.7671	$35.77	$35.75	$35.80
7 purchase totals =	$553.76		$602.4868	$602.48	$602.50	$602.50