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	$49.92	13.673%	$56.7456	$56.75	$56.75	$56.70
Purchase #2	$120.42	8.726%	$130.9278	$130.93	$130.95	$130.90
Purchase #3	$162.71	13.583%	$184.8109	$184.81	$184.80	$184.80
Purchase #4	$80.71	11.802%	$90.2354	$90.24	$90.25	$90.20
Purchase #5	$93.44	5.724%	$98.7885	$98.79	$98.80	$98.80
Purchase #6	$183.73	13.831%	$209.1417	$209.14	$209.15	$209.10
Purchase #7	$246.46	13.618%	$280.0229	$280.02	$280.00	$280.00
7 purchase totals =	$937.39		$1,050.6728	$1,050.68	$1,050.70	$1,050.50