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	$160.69	11.368%	$178.9572	$178.96	$178.95	$179.00
Purchase #2	$53.73	5.760%	$56.8248	$56.82	$56.80	$56.80
Purchase #3	$101.82	8.124%	$110.0919	$110.09	$110.10	$110.10
Purchase #4	$52.71	13.233%	$59.6851	$59.69	$59.70	$59.70
Purchase #5	$195.60	13.630%	$222.2603	$222.26	$222.25	$222.30
Purchase #6	$93.53	8.450%	$101.4333	$101.43	$101.45	$101.40
Purchase #7	$156.61	7.266%	$167.9893	$167.99	$168.00	$168.00
7 purchase totals =	$814.69		$897.2419	$897.24	$897.25	$897.30