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	$82.58	6.565%	$88.0014	$88.00	$88.00	$88.00
Purchase #2	$168.73	10.594%	$186.6053	$186.61	$186.60	$186.60
Purchase #3	$110.91	11.196%	$123.3275	$123.33	$123.35	$123.30
Purchase #4	$218.42	6.773%	$233.2136	$233.21	$233.20	$233.20
Purchase #5	$46.53	10.509%	$51.4198	$51.42	$51.40	$51.40
Purchase #6	$136.48	3.502%	$141.2595	$141.26	$141.25	$141.30
Purchase #7	$167.55	3.501%	$173.4159	$173.42	$173.40	$173.40
7 purchase totals =	$931.20		$997.2430	$997.25	$997.20	$997.20