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	$209.80	13.849%	$238.8552	$238.86	$238.85	$238.90
Purchase #2	$48.54	11.800%	$54.2677	$54.27	$54.25	$54.30
Purchase #3	$125.35	11.681%	$139.9921	$139.99	$140.00	$140.00
Purchase #4	$157.81	10.529%	$174.4258	$174.43	$174.45	$174.40
Purchase #5	$139.61	8.792%	$151.8845	$151.88	$151.90	$151.90
Purchase #6	$89.57	4.550%	$93.6454	$93.65	$93.65	$93.60
Purchase #7	$144.60	13.424%	$164.0111	$164.01	$164.00	$164.00
7 purchase totals =	$915.28		$1,017.0818	$1,017.09	$1,017.10	$1,017.10