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	$131.33	11.491%	$146.4211	$146.42	$146.40	$146.40
Purchase #2	$217.96	12.522%	$245.253	$245.25	$245.25	$245.30
Purchase #3	$166.52	9.592%	$182.4926	$182.49	$182.50	$182.50
Purchase #4	$170.88	12.352%	$191.9871	$191.99	$192.00	$192.00
Purchase #5	$126.67	9.614%	$138.8481	$138.85	$138.85	$138.80
Purchase #6	$120.56	6.711%	$128.6508	$128.65	$128.65	$128.70
Purchase #7	$73.58	6.357%	$78.2575	$78.26	$78.25	$78.30
7 purchase totals =	$1,007.50		$1,111.9102	$1,111.91	$1,111.90	$1,112.00