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	$72.26	13.462%	$81.9876	$81.99	$82.00	$82.00
Purchase #2	$167.50	10.376%	$184.8798	$184.88	$184.90	$184.90
Purchase #3	$172.72	9.774%	$189.6017	$189.60	$189.60	$189.60
Purchase #4	$61.92	4.636%	$64.7906	$64.79	$64.80	$64.80
Purchase #5	$100.59	3.196%	$103.8049	$103.80	$103.80	$103.80
Purchase #6	$108.33	9.475%	$118.5943	$118.59	$118.60	$118.60
Purchase #7	$84.35	12.366%	$94.7807	$94.78	$94.80	$94.80
7 purchase totals =	$767.67		$838.4396	$838.43	$838.50	$838.50