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	$80.65	3.329%	$83.3348	$83.33	$83.35	$83.30
Purchase #2	$101.43	10.299%	$111.8763	$111.88	$111.90	$111.90
Purchase #3	$64.33	9.233%	$70.2696	$70.27	$70.25	$70.30
Purchase #4	$136.32	4.143%	$141.9677	$141.97	$141.95	$142.00
Purchase #5	$159.78	13.270%	$180.9828	$180.98	$181.00	$181.00
Purchase #6	$97.72	4.769%	$102.3803	$102.38	$102.40	$102.40
Purchase #7	$230.80	6.377%	$245.5181	$245.52	$245.50	$245.50
7 purchase totals =	$871.03		$936.3296	$936.33	$936.35	$936.40