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	$231.79	11.730%	$258.979	$258.98	$259.00	$259.00
Purchase #2	$244.59	10.119%	$269.3401	$269.34	$269.35	$269.30
Purchase #3	$83.59	3.655%	$86.6452	$86.65	$86.65	$86.60
Purchase #4	$48.40	12.129%	$54.2704	$54.27	$54.25	$54.30
Purchase #5	$36.58	10.377%	$40.3759	$40.38	$40.40	$40.40
Purchase #6	$177.83	12.478%	$200.0196	$200.02	$200.00	$200.00
Purchase #7	$230.64	13.454%	$261.6703	$261.67	$261.65	$261.70
7 purchase totals =	$1,053.42		$1,171.3005	$1,171.31	$1,171.30	$1,171.30