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	$170.49	9.523%	$186.7258	$186.73	$186.75	$186.70
Purchase #2	$234.70	10.111%	$258.4305	$258.43	$258.45	$258.40
Purchase #3	$116.25	12.498%	$130.7789	$130.78	$130.80	$130.80
Purchase #4	$160.39	10.311%	$176.9278	$176.93	$176.95	$176.90
Purchase #5	$36.94	3.551%	$38.2517	$38.25	$38.25	$38.30
Purchase #6	$178.43	7.346%	$191.5375	$191.54	$191.55	$191.50
Purchase #7	$35.33	4.758%	$37.011	$37.01	$37.00	$37.00
7 purchase totals =	$932.53		$1,019.6632	$1,019.67	$1,019.75	$1,019.60