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	$7.26	3.604%	$7.5217	$7.52	$7.50	$7.50
Purchase #2	$245.91	5.116%	$258.4908	$258.49	$258.50	$258.50
Purchase #3	$82.90	12.298%	$93.095	$93.10	$93.10	$93.10
Purchase #4	$160.92	11.404%	$179.2713	$179.27	$179.25	$179.30
Purchase #5	$162.80	3.115%	$167.8712	$167.87	$167.85	$167.90
Purchase #6	$135.72	6.509%	$144.554	$144.55	$144.55	$144.60
Purchase #7	$228.79	4.667%	$239.4676	$239.47	$239.45	$239.50
7 purchase totals =	$1,024.30		$1,090.2716	$1,090.27	$1,090.20	$1,090.40