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	$178.42	6.375%	$189.7943	$189.79	$189.80	$189.80
Purchase #2	$63.91	4.216%	$66.6044	$66.60	$66.60	$66.60
Purchase #3	$180.57	6.575%	$192.4425	$192.44	$192.45	$192.40
Purchase #4	$145.45	7.257%	$156.0053	$156.01	$156.00	$156.00
Purchase #5	$63.65	12.299%	$71.4783	$71.48	$71.50	$71.50
Purchase #6	$54.96	11.433%	$61.2436	$61.24	$61.25	$61.20
Purchase #7	$250.93	4.556%	$262.3624	$262.36	$262.35	$262.40
7 purchase totals =	$937.89		$999.9308	$999.92	$999.95	$999.90