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	$148.28	3.288%	$153.1554	$153.16	$153.15	$153.20
Purchase #2	$123.62	10.716%	$136.8671	$136.87	$136.85	$136.90
Purchase #3	$136.69	10.286%	$150.7499	$150.75	$150.75	$150.70
Purchase #4	$74.98	13.771%	$85.3055	$85.31	$85.30	$85.30
Purchase #5	$186.58	13.193%	$211.1955	$211.20	$211.20	$211.20
Purchase #6	$25.63	6.602%	$27.3221	$27.32	$27.30	$27.30
Purchase #7	$75.27	9.405%	$82.3491	$82.35	$82.35	$82.30
7 purchase totals =	$771.05		$846.9446	$846.96	$846.90	$846.90