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	$96.36	6.204%	$102.3382	$102.34	$102.35	$102.30
Purchase #2	$58.53	13.481%	$66.4204	$66.42	$66.40	$66.40
Purchase #3	$138.91	12.493%	$156.264	$156.26	$156.25	$156.30
Purchase #4	$158.38	9.844%	$173.9709	$173.97	$173.95	$174.00
Purchase #5	$136.70	13.432%	$155.0615	$155.06	$155.05	$155.10
Purchase #6	$160.67	11.732%	$179.5198	$179.52	$179.50	$179.50
Purchase #7	$82.72	9.822%	$90.8448	$90.84	$90.85	$90.80
7 purchase totals =	$832.27		$924.4196	$924.41	$924.35	$924.40