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	$137.34	7.410%	$147.5169	$147.52	$147.50	$147.50
Purchase #2	$198.59	12.787%	$223.9837	$223.98	$224.00	$224.00
Purchase #3	$139.63	12.179%	$156.6355	$156.64	$156.65	$156.60
Purchase #4	$181.95	5.479%	$191.919	$191.92	$191.90	$191.90
Purchase #5	$239.28	7.379%	$256.9365	$256.94	$256.95	$256.90
Purchase #6	$105.86	10.469%	$116.9425	$116.94	$116.95	$116.90
Purchase #7	$193.45	11.466%	$215.631	$215.63	$215.65	$215.60
7 purchase totals =	$1,196.10		$1,309.5651	$1,309.57	$1,309.60	$1,309.40