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	$174.27	4.187%	$181.5667	$181.57	$181.55	$181.60
Purchase #2	$238.52	4.865%	$250.124	$250.12	$250.10	$250.10
Purchase #3	$143.47	3.731%	$148.8229	$148.82	$148.80	$148.80
Purchase #4	$53.83	12.509%	$60.5636	$60.56	$60.55	$60.60
Purchase #5	$15.82	6.524%	$16.8521	$16.85	$16.85	$16.90
Purchase #6	$60.41	12.575%	$68.0066	$68.01	$68.00	$68.00
Purchase #7	$98.42	13.181%	$111.3927	$111.39	$111.40	$111.40
7 purchase totals =	$784.74		$837.3286	$837.32	$837.25	$837.40