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	$19.53	4.716%	$20.451	$20.45	$20.45	$20.50
Purchase #2	$110.41	3.524%	$114.3008	$114.30	$114.30	$114.30
Purchase #3	$27.99	12.763%	$31.5624	$31.56	$31.55	$31.60
Purchase #4	$96.53	11.124%	$107.268	$107.27	$107.25	$107.30
Purchase #5	$230.96	8.465%	$250.5108	$250.51	$250.50	$250.50
Purchase #6	$153.49	7.155%	$164.4722	$164.47	$164.45	$164.50
Purchase #7	$187.49	4.801%	$196.4914	$196.49	$196.50	$196.50
7 purchase totals =	$826.40		$885.0566	$885.05	$885.00	$885.20