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	$84.42	13.175%	$95.5423	$95.54	$95.55	$95.50
Purchase #2	$111.55	11.138%	$123.9744	$123.97	$123.95	$124.00
Purchase #3	$230.90	8.335%	$250.1455	$250.15	$250.15	$250.10
Purchase #4	$248.71	8.758%	$270.492	$270.49	$270.50	$270.50
Purchase #5	$168.89	12.164%	$189.4338	$189.43	$189.45	$189.40
Purchase #6	$190.72	10.238%	$210.2459	$210.25	$210.25	$210.20
Purchase #7	$139.62	6.762%	$149.0611	$149.06	$149.05	$149.10
7 purchase totals =	$1,174.81		$1,288.8950	$1,288.89	$1,288.90	$1,288.80