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	$131.56	5.704%	$139.0642	$139.06	$139.05	$139.10
Purchase #2	$104.68	9.739%	$114.8748	$114.87	$114.85	$114.90
Purchase #3	$37.57	13.357%	$42.5882	$42.59	$42.60	$42.60
Purchase #4	$154.82	11.217%	$172.1862	$172.19	$172.20	$172.20
Purchase #5	$167.39	8.424%	$181.4909	$181.49	$181.50	$181.50
Purchase #6	$46.74	13.740%	$53.1621	$53.16	$53.15	$53.20
Purchase #7	$175.89	5.182%	$185.0046	$185.00	$185.00	$185.00
7 purchase totals =	$818.65		$888.3710	$888.36	$888.35	$888.50