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	$155.97	3.158%	$160.8955	$160.90	$160.90	$160.90
Purchase #2	$47.95	9.240%	$52.3806	$52.38	$52.40	$52.40
Purchase #3	$139.69	3.469%	$144.5358	$144.54	$144.55	$144.50
Purchase #4	$234.27	4.641%	$245.1425	$245.14	$245.15	$245.10
Purchase #5	$144.34	4.108%	$150.2695	$150.27	$150.25	$150.30
Purchase #6	$152.75	8.664%	$165.9843	$165.98	$166.00	$166.00
Purchase #7	$174.84	10.253%	$192.7663	$192.77	$192.75	$192.80
7 purchase totals =	$1,049.81		$1,111.9745	$1,111.98	$1,112.00	$1,112.00