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	$242.28	10.649%	$268.0804	$268.08	$268.10	$268.10
Purchase #2	$215.43	12.568%	$242.5052	$242.51	$242.50	$242.50
Purchase #3	$74.95	10.398%	$82.7433	$82.74	$82.75	$82.70
Purchase #4	$98.32	13.122%	$111.2216	$111.22	$111.20	$111.20
Purchase #5	$179.31	11.102%	$199.217	$199.22	$199.20	$199.20
Purchase #6	$40.38	8.714%	$43.8987	$43.90	$43.90	$43.90
Purchase #7	$212.32	3.219%	$219.1546	$219.15	$219.15	$219.20
7 purchase totals =	$1,062.99		$1,166.8208	$1,166.82	$1,166.80	$1,166.80