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	$39.69	7.216%	$42.554	$42.55	$42.55	$42.60
Purchase #2	$154.30	9.836%	$169.4769	$169.48	$169.50	$169.50
Purchase #3	$126.53	13.695%	$143.8583	$143.86	$143.85	$143.90
Purchase #4	$154.64	7.158%	$165.7091	$165.71	$165.70	$165.70
Purchase #5	$101.61	11.648%	$113.4455	$113.45	$113.45	$113.40
Purchase #6	$142.78	9.523%	$156.3769	$156.38	$156.40	$156.40
Purchase #7	$209.52	5.123%	$220.2537	$220.25	$220.25	$220.30
7 purchase totals =	$929.07		$1,011.6744	$1,011.68	$1,011.70	$1,011.80