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	$249.63	8.723%	$271.4052	$271.41	$271.40	$271.40
Purchase #2	$78.64	13.615%	$89.3468	$89.35	$89.35	$89.30
Purchase #3	$91.62	12.424%	$103.0029	$103.00	$103.00	$103.00
Purchase #4	$172.54	8.293%	$186.8487	$186.85	$186.85	$186.80
Purchase #5	$156.80	5.790%	$165.8787	$165.88	$165.90	$165.90
Purchase #6	$29.58	6.341%	$31.4557	$31.46	$31.45	$31.50
Purchase #7	$211.28	10.688%	$233.8616	$233.86	$233.85	$233.90
7 purchase totals =	$990.09		$1,081.7996	$1,081.81	$1,081.80	$1,081.80